Tool Identification

The identification of tools produced by Duro and Indestro presents some challenges, partly due to the dual company structure but mostly because of their extensive contract production activities. In a previous section we reviewed the various registered trademarks used by the companies, which of course when used provide positive identification. In this section we will examine various informal marks and brands, certain characteristic marking styles, and some of the production characteristics that can help pinpoint Duro and Indestro.

Where possible, the figures will show combinations of an informal mark with a registered trademark, in order to establish a firm connection with the companies' products.

We'll begin this section with the two logo designs used by the company.

D-Trapezoid Logo

Fig. 20. D-Trapezoid Logo.

Fig. 20 shows the D-Trapezoid logo marked on an early Duro socket.

This logo is a truncated triangle representing a stylized "D" for Duro and was used as the marking on early Duro sockets.

More information on the origin of this marking can be found in the section on the D-Trapezoid Marking.

X-Circle Logo

Fig. 21. X-Circle Logo.

Fig. 21 shows the X-Circle logo stamped on a tool, representing a stylized "DC" butted together in a circle.

This logo was stamped on tools during the wartime period in place of the normal "Duro-Chrome" marking.

More information on the origin of this marking can be found in the section on the X-Circle Marking.

Informal Brands

Indestro made use of a number of informal brands, including Chromium Vanadium, Indestro Polygon, Super-Quality, Indestro Super, and Select Steel. These brands evolved in a relatively compressed time frame from 1931 to 1945, after which Indestro Super or Select Steel accounted for most of their ongoing production. ("Select Steel Tools" was actually filed as a trademark in the 1960s.)

In contrast, Duro used its registered trademark Duro-Chrome as its primary brand, with Duro-Bilt (also registered) appearing briefly on socket sets in the late 1920s and early 1930s. However, some early production of box wrenches for Western Auto was marked with an informal "Perfection" brand, and Duro used "Handy-Hex" as a brand for box-end wrenches from the early 1930s until around 1936.

Chromium Vanadium

By 1931 Indestro had started using the mark "Chromium Vanadium" on tools made as contract production for Western Auto Supply. The use of this phrase (with the element names spelled out) was unusual, as most manufacturers would use the abbreviated form chrome-vanadium for the alloy.

We have strong evidence for the 1931 date, both from the Western Auto catalogs and from the fortunate acquisition of an early Indestro "Chromium Vanadium" socket set with a dated sales receipt from 1931 — and from a Western Auto store no less! The set consists of ten 12-point sockets, a speeder, sliding Tee handle, ratchet adapter, extensions, and a universal, with most of the pieces being marked "Chromium Vanadium". The speeder is also marked "Indestro Chicago", and the metal box has an Indestro decal on the top.

The set was purchased from a Western Auto store, and a check of their 1931 and 1932 catalogs found that a "Chromium Vanadium" socket set was available, with a description exactly matching the set as acquired.

Fig. 22. Indestro "Chromium Vanadium" 1/2-Drive Speeder, with Insets for Detail, 1931.

Fig. 22 shows the Indestro speeder from the 17-piece set, stamped "Chromium Vanadium" on the shank, with Indestro Mfg. Co." and "Chicago, U.S.A." on the back side.

The full set can be seen as the Indestro 17-Piece Socket Set.

The Western Auto Supply connection provides an explanation for Indestro's use of the "Chromium Vanadium" mark — Western Auto had begun using "Chromium Vanadium" as a brand in its catalogs in 1931, and as a supplier to Western Auto, Indestro needed to mark their production for Western Auto accordingly. But since Indestro was working primarily with chrome-vanadium steel anyway, they probably found it easier to just mark all of their alloy tools with "Chromium Vanadium".

Fig. 23. Indestro "Chromium-Vanadium" 1/4-Drive Socket Set, ca. 1935-1936.

Fig. 23 shows an Indestro "Chromium-Vanadium" 1/4-drive 11-piece socket set, with "Chromium-Vanadium" prominently featured in the logo decal.

In this set the individual tools are not marked except for sizes on the sockets.

This next figure shows a group of three somewhat later sockets with the "Chromium Vanadium" marking.

The 1938 Duro catalog lists a 12xx series of 1/2 drive 12-point (and 8-point) sockets that it refers to as "Chrome Vanadium sockets", with model numbers that would later become the Indestro Super line. At this time they were marked with "Chromium Vanadium" and the model number, as shown in Fig. 24 below.

Fig. 24. Chromium Vanadium Sockets, Left to Right: 2812, 1220S, 1234.

The model 1234 socket on the right is believed to date to the mid 1930s, as it shows the cross-hatched knurling in use at this time. Later on these models changed to the simpler straight knurling shown on the middle and left sockets.

The 1220S number on the middle socket indicates an 8-point broaching.

The leftmost socket is a model 2812 1/4-drive 3/8 socket. Although this model is not shown in the 1938 catalog, a later Indestro catalog lists 2812 as part of the Indestro Super 1/4 drive line. This again confirms the continuity of the "Chromium Vanadium" mark with the later Indestro Super line, with a likely "Super-Quality" intermediate.

Indestro Polygon

The Indestro "Polygon" brand was in use around the same time as the "Chromium Vanadium" mark, and currently the known examples are all offset box-end wrenches. The "Polygon" wrenches are very similar to the "Perfection" wrenches made by Duro as contract production for Western Auto, so we can regard these as a rebranding for Indestro.

Currently all of the "Polygon" wrenches we've seen were also marked for Indestro, leaving no uncertainty as to the maker. But if examples were made without the company marking, the "Polygon" brand and production characteristics should be sufficient to identify the maker.

Although the dates are uncertain, the Indestro "Polygon" wrenches were probably made beginning with the Duro-Indestro merger in 1933 and continuing into the mid 1930s. The "Polygon" wrenches are believed to have been sold primarily through Western Auto Supply as the lower-cost "Standard" version of its box-end wrenches.

Fig. 25. Indestro "Polygon" 5/8x11/16 Offset Box-End Wrench, with Insets for Side View and Back Side Detail, ca. 1933 to Early 1930s.

Fig. 25 shows an Indestro "Polygon" 5/8x11/16 offset box wrench, stamped "Chromium-Vanadium" on the back side.

The overall length is 9.8 inches, and the finish is polished steel.

The upper inset shows a side view of the wrench to illustrate the construction details. The shank is roughly oval in cross-section, with a smoothly rounded top and bottom and clipped sides.

A particular detail to note is that the offset shank joins the box end over the full width of the box, without a lip above and below the join.

Later construction for Duro and Indestro offset box wrenches generally had the shank joining near the middle of the box end, with a distinct lip above and below. See for example the Indestro Super 731A Wrench shown later in this page.

Fig. 26. Indestro "Polygon" Wrenches with "Chromium-Vanadium" Mark.

Fig. 26 illustrates the connection between the "Polygon" and "Chromium-Vanadium" marks, showing the back side of three Indestro "Polygon" wrenches.

Super-Quality

By 1935 Indestro had started using the phrase "Super-Quality" as a brand for its chrome alloy tools. This use of "Super-Quality" is the obvious forerunner for the eventual Indestro "Super" line.

Fig. 27. Indestro Socket Set of Chrome Vanadium Steel with "Super-Quality" Logo.

Fig. 27 provides an example, a 1/4-drive socket set with an Indestro logo showing "Super-Quality" and "Chrome Vanadium Steel".

The tools in this set are marked "Chromium Vanadium", and some have part numbers that in later catalogs would be identified as part of the Indestro "Super" line.

Although the date of the first use of "Super-Quality" is unknown, the mark was definitely in use by 1935, as the 1935 Indestro catalog shows a number of examples. In this early usage the "Super-Quality" mark referred not only to the use of alloy steel, but to a premium triple-plated finish as well. Tools with lesser finishes were typically marked with a leading "0" on the model number.

A 1941 Indestro catalog shows extensive use of the "Super-Quality" mark for the chrome alloy tools, both on the tool illustrations and on advertising displays. Interestingly, the sockets shown are referred to as "Super-Quality" in the text but are marked "Chromium Vanadium" in the illustrations, suggesting that the change may have been phased in over a period of time.

Fig. 28. Duro-Chrome and Indestro Wrenches with Super-Quality and X-Circle Marks.

In Fig. 28 we see several more examples of the use of the "Super-Quality" mark, this time on the tools themselves, along with other identifying marks.

The wrench at the top is marked Indestro and has the part number 714, which later catalogs show as part of the Indestro Super line. Note that this wrench does not have the streamlined panels of the other three, suggesting that the Super-Quality mark was in use before the 1937 "Streamline" trademark.

The two middle wrenches are marked with "Super-Quality" and the X-Circle mark, and in addition show the streamlined design in the polished raised panel area.

The bottom wrench is marked Duro-Chrome 2013 and shows the X-Circle mark as well. The raised panel streamlined design is comparable to that in the middle two wrenches, showing the commonality of design among the tools.

Fig. 29. Indestro 763 9/16x5/8 S-Shaped Box-End Wrenches, with Inset for Back Side Detail.

Fig. 29 shows another example of the "Super-Quality" mark, an Indestro 763 9/16x5/8 S-shaped box-end wrench marked "U.S.A." and "Super-Quality".

The inset shows the back side with "Chrome Vanadium Steel" in a particular slanted font, which will be discussed in a later section.

Indestro Super

We've mentioned the "Indestro Super" brand several times as the successor to the Super-Quality mark, so for completeness we'll show some examples. Note though that identification is never a problem with this brand, as the Indestro company name is always present in this mark, unlike the case with Super-Quality.

The transition date from Super-Quality to Indestro Super is a bit uncertain, as we currently don't have sufficient catalog coverage or other information. However, the first example below at least suggests a likely time frame of 1944-1945.

Fig. 30. Indestro Super [T-] 2 1/2x9/16 Tappet Wrench, with Inset for Back Side Detail, ca. 1944-1945.

Fig. 30 shows an Indestro [T-] 2 1/2x9/16 tappet wrench, stamped "Indestro Super" on the face with "Forged in U.S.A." on the back side.

The finish is plain steel with traces of the original cadmium plating, and this provides a helpful clue to the manufacturing date.

Indestro and Duro-Chrome wrenches were generally given chrome plated finishes after the early 1930s, except for the period of wartime shortages in 1944-1945. Tools made at that time generally substituted cadmium (or plain) finishes for chrome, so it's likely that this wrench was made in 1944-1945.

This tool is probably our earliest example of the Indestro Super marking, and indicates that the transition likely occurred around that time.

Fig. 31. Indestro Super 731A 9/16x5/8 Offset Box-End Wrench, with Insets for Side View and Back Side Detail.

Our next example is shown in Fig. 31, an Indestro Super 731A 9/16x5/8 offset box-end wrench. The hexagonal shank has raised panels in the streamlined design, with "Indestro Super" on the front and "Forged in U.S.A." on the back side.

Select Steel

Duro and Indestro began using the phrase "Select Steel" in several variations as an informal trademark fairly early on, probably as soon as they needed to make a distinction between the more expensive chrome alloy steel and the less expensive "Select" alloy. Many of their tools are marked with the phrases "Forged Select Steel" or "Drop Forged Select Steel" (or other variations), and the catalogs have a section for "Select Steel" economy tools as well as the high-end "Chrome Alloy" tools. (As previously noted in the section on trademarks, Indestro did later register "Select Steel Tools" as a formal trademark.)

Fig. 32. Indestro Chicago Wrenches with "Drop Forged Select Steel".

Fig. 32 shows the use of "Drop Forged Select Steel" on the back side of the Indestro Chicago wrenches, previously shown in the discussion of the Streamlined Design Trademark.

With the history of consistent use of "Select Steel" as a brand, this should serve as a clear identification for Indestro tools, especially when present with other distinctive marks.

Perfection

By 1932 Duro was producing a series of "Perfection" offset box wrenches for Western Auto Supply, marked with "Chromium Vanadium" on the back side. These wrenches were designed as copies of Herbrand's "Multihex" box wrenches, as Duro attempted (successfully) to win more business from Western Auto.

The Perfection marking appears to have been used only briefly, after which the wrenches were marked with just "Chromium Vanadium".

An example of this marking can be seen as the Perfection P-27 Offset Box Wrench in our section on contract production.

Handy-Hex

The next figure shows the tool that proved to be the "missing link" to a brand name used by Duro in the early to mid 1930s. The front side of the wrench is clearly marked as Duro-Chrome model number 268, which is listed as a chrome vanadium brake wrench (Ford-specific) in catalog 38M and others. But on the back side (see inset), it's also marked as "Handy-Hex".

Prior to the discovery of this wrench, the "Handy-Hex" mark had been the source of a long-standing mystery, as a number of wrenches of this brand had been acquired, but no references had been found to identify the maker.

Fig. 33. Duro-Chrome 268 7/16x1/2 8-Point Brake Wrench, with Inset Showing "Handy-Hex" Brand.

Fig. 33 shows a Duro-Chrome 268 7/16x1/2 8-point brake wrench, marked "Chrome Vanadium Steel" with "Ford Brakes" and "Handy-Hex" on the back side.

The overall length is 11.0 inches.

After this wrench turned up, the markings on some older Handy-Hex pieces were reexamined to look for previously missed clues. Two of the available examples were deep-offset wrenches marked "Chrome Vanadium Steel", with model numbers 02055 (13/16 x 7/8) and 02056 (15/16 x 1). (One of these Handy-Hex wrenches is shown in below.)

When the Duro-Chrome catalog 38M was checked for this style of deep offset wrench, it listed model number 2055 with sizes 13/16x7/8, model 2056 with sizes 15/16x1, and an overlooked caption jumped out: "Handy-Twin-Hex"!

Fig. 34. Handy-Hex 02055 13/16x7/8 Wrench, with Inset for Back Side Detail.

Fig. 34 shows a Handy-Hex 02055 13/16x7/8 offset box wrench, marked "Made in U.S.A." with "Chrome Vanadium Steel" on the back side.

The overall length is 12.6 inches, and the finish is a thin plating with a yellowish tint.

Marking Characteristics

Duro and Indestro had some very specific marking styles or quirks that may help to identify their tools, particularly when found in conjunction with other distinctive marks.

Slanted Font with "Chrome Vanadium Steel"

One important identifier for Indestro tools is the use of the phrase "Chrome Vanadium Steel" (or "Chromium Vanadium Steel") in a distinctive slanted font. This next figure shows an example.

Fig. 35. Indestro 769 9/16x5/8 Half-Moon Wrench, with Inset Showing Slanted Font.

Fig. 35 shows an Indestro 769 9/16x5/8 half-moon wrench, marked "U.S.A." with "Super-Quality" on the front side. The inset shows the back side with an example of "Chrome Vanadium Steel" in the slanted font.

Although this slanted font could have been used by other manufacturers, currently the only examples known are on tools marked as Indestro, or of apparent Indestro production. (Tools marked with Duro brands or model numbers have not been observed to use the slanted font.)

Another example of the slanted font can be seen on the Indestro 763 S-Shaped Wrench.

Curved Arc "Forged in U.S.A." Mark

Another marking style noted only on Duro/Indestro tools is the use of the phrase "Forged in U.S.A." curved along a circular arc, typically stamped on a wrench head.

Fig. 36. 1935 Catalog Illustration of Curved Arc "Forged in U.S.A." Mark.

The scan in Fig. 36 shows an excerpt from page 8 of the 1935 Duro catalog, and the illustration confirms that the curved-arc marking was in use at that time.

An even earlier example can be seen in contract production for the "Cross Country" brand from the 1933-1934 time frame.

Other companies generally use markings arranged in a straight line, so the curved arc marking style strongly indicates Duro/Indestro production.

Fig. 37. Curved Arc "Forged in U.S.A." Mark on Several Duro-Chrome Wrenches.

Fig. 37 shows several examples of Duro-Chrome wrenches with a "Forged in U.S.A." marking along a curved arc.

Examples of this marking have been found on tools marked "Duro-Chrome", "Super-Quality" and "Indestro Super", or otherwise marked to indicate an alloy steel tool, but not on economy-grade Select Steel tools.

Numerous other examples of this marking can be found throughout this article.

Fig. 38. Cross Country 1831 3/4x3/4 Angle-Head Obstruction Wrench, with Inset for Back Side Detail, ca. 1933-1934.

Fig. 38 shows a Cross Country 1831 3/4x3/4 angle-head obstruction wrench, stamped "Chrome Vanadium Steel" on the front face, with "Forged in U.S.A." along a curved arc on the back side, as shown in the inset.

This wrench is readily identified as Duro production by the 1831 model number and curved-arc "Forged in U.S.A." marking.

With its 1933-1934 production date, this wrench is currently our earliest example of the curved-arc marking.

The X-Circle Mark

We've seen several examples of the X-Circle mark previously (e.g. on Super-Quality Wrenches) and will now examine this marking more closely.

Fig. 39. Duro-Chrome 2015A 13/16x7/8 Box-End Wrench, with Insets for Back Side and X-Circle Logo.

Fig. 39 shows a Duro-Chrome 2015A 13/16x7/8 box-end wrench, stamped with a somewhat larger than normal X-Circle along with the usual markings.

Although no documentation for the origin of this mark has been found, a close examination of the logo in Fig. 39 suggests its likely meaning. Note that the sides of the "X" are actually curved, so that the mark resembles the letters "DC" butted together, with the circle overstriking the left edge of the "D". Thus the mark is likely intended as a stylized "DC" representing Duro-Chrome, similar to the NB-Circle logo used by New Britain with its "None Better" trademark. We'll refer to this mark as the X-Circle logo in the text.

Since the X-Circle marking is almost always found on tools with plain finishes or other signs of wartime production, this mark is presumed to be Duro's identification for tools produced under wartime contracts. Further examples of the X-Circle mark can be found in the section on Duro/Indestro Wartime Production.

Fig. 40. Duro-Chrome 2081 9/16x5/8 Half-Moon Box Wrench, with Inset for Back Side.

Fig. 40 shows another example of the X-Circle mark, this time on a Duro-Chrome 2081 9/16x5/8 half-moon wrench, marked "Forged in U.S.A." with "Manifold & Starter" and an X-Circle on the back side.

The overall length is 7.2 inches, and the finish is plain steel.

This style of wrench is referred to as an "elbow wrench" in the Duro catalogs. The Indestro 769 model is nearly identical except for markings.

Based on the observed patterns of usage, the X-Circle mark was used to indicate production under Duro's government contracts during the 1942-1945 wartime years. The main evidence for this interpretation is that tools with the X-Circle mark are generally observed with plain or cadmium finishes, or with other signs of wartime production, such as roughly milled faces on open-end wrenches.

Some tools were marked with X-Circle as the only indication of the company, but in other cases the X-Circle mark appears along with a Duro-Chrome or Super-Quality brand. These latter examples can be interpreted as production originally intended for civilian markets, but diverted to a government contract in order to meet production quotas.

Patent Numbers and Dates

Patent numbers and dates can be extremely valuable for identifying tools. Duro Metal Products was quite prolific in its patent activities, as we saw in the Patent Table shown in the previous section. The tools produced under these patents were often marked with the patent number or date, and such patent markings may then serve as an important identification mark.

The figures below will show some examples of Duro and Indestro tools with patent markings.

In some cases the patent number may be the only identifying mark on a tool, perhaps to allow the tool to sell with various private brandings, or with no other identification at all.

Fig. 41. Duro 672 1/2-Drive Ratchet Handles with Patent #1,798,481.

An example of this is shown in Fig. 41, where we see three similar examples of the Duro model 672, an early ratchet handle.

The ratchet at the top is marked "Duro Metal Products Co. 672" and "Patent Pending", and the one in the middle is similarly marked, except that it shows the actual patent #1,798,481.

The ratchet on the bottom is identical to the other two and shows the same patent number, but is marked with just "Chicago, U.S.A.", without a maker or model number.

The explanation is simple: the bottom ratchet came from an Indestro-branded socket set, and in order to maintain the separation of the brand names, Indestro simply omitted the Duro branding and model number.

The patent information on these ratchet handles provides an opportunity to estimate the production date of a tool. The first ratchet handle, being marked "Patent Pending", would have been made during the interval between the filing of the patent application and the subsequent issue. The other ratchets are marked with the actual patent number, so by examining the document for patent #1,798,481, we can determine that the first ratchet was likely made between 1928 and 1931.

Fig. 42. An Indestro No. 1351 Socket Set, with Inset Showing Patent #1,788,535.

Fig. 42 shows an example of a socket set identified only by a patent number, in this case the Duro Metal patent #1,788,535. After reviewing an Indestro catalog, the socket set matches the description and appearance of model No. 1351, but none of the tools are marked with a company name or part number.

However, the bottom of the case is stamped with the patent number, as shown in the inset. (The vintage price sticker is interesting as well.)

Fig. 43. Duro 1/2-Hex Drive L-T Convertible Handle with Patent #1,744,413.

Fig. 43 shows a Duro 1/2-hex drive convertible L-T handle, a tool frequently included in Duro and Indestro economy-line socket sets.

The handle is marked only with "Made in U.S.A" and "Pat. No. 1,744,413", with the omission of the company name suggesting that the tool was probably intended for contract production.

This handle was acquired as part of a socket set in a box with a sliding lid.

The patent #1,744,413 was issued in 1930 to E.H. Peterson, one of Duro's most active inventors. In operation, the tool converts to a Tee-handle by sliding the Ell-handle bar out of the sheath, then inserting the short arm of the Ell into the side of the sheath. The arm locks in place against an indentation in the wall of the sheath.

The Duro L-T handle was also made in a 1/2-drive version as the Duro No. 660 1/2-Drive L-T Handle. The No. 660 L-T handle was used in a number of early Duro/Indestro socket sets, including sets sold by Sears Roebuck under the Durobilt brand. The Duro L-T tool is similar in operation to the Hinsdale Convertible T-L Handle, except that the Hinsdale tool is permanently assembled.

One of the more notable Duro inventions described a novel way for constructing ratchets, and was issued as patent #1,902,878 in 1933. Instead of the conventional ratchet assembly held together with screws or rivets, the Duro design secured the parts with a pressed flange integral to the forging. This allowed Duro to produce a high-quality forged ratchet at a reasonably low cost, and the resulting products were sold widely into high-volume markets.

Fig. 44. Duro-Chrome 678D 1/2-Drive Ratchet with Patent #1,902,878.

Fig. 44 an example of the pressed-flange design, a 1/2-drive Duro-Chrome model 678D reversible ratchet, marked with a bold "Duro-Chrome" on a raised panel in the center of the forged handle. The back side shows a similar panel with "Made in U.S.A." and "Pat. No. 1902878".

The overall length is 10.4 inches, and the finish is plain steel with a dark oxide coating.

Fig. 45. Duro-Chrome 4487 1/4-Drive Ratchet with Patent #1,902,878.

The pressed-flange construction was also used for other drive sizes, as can be seen in Fig. 45, a 1/4-drive Duro-Chrome model 4487 ratchet.

The handle has a forged "Duro-Chrome" on a raised panel, and a similar panel is marked "Made in U.S.A." and "Pat. No. 1902878" on the back side.

Fig. 46. Duro-Chrome 2114 Battery Pliers with Patent #D119,441.

The next figure shows a pair of battery pliers with unusual box-end wrench handles, marked with a design patent.

In Fig. 46 we see the Duro-Chrome 2114 battery pliers, marked "Forged in U.S.A." with "Des. 119,441" for the design patent.

The design patent #D119,441 was issued on March 12, 1940 to W.A. Sandy and assigned to Duro Metal Products.

"Star" Marking on Indestro Sockets

The early sockets produced by Indestro are frequently difficult to identify, as they were typically marked with only the fractional size and possibly a star symbol. In some cases, the only guide to the maker is the overall design and construction of the socket.

From the mid 1920s onward Indestro was producing hex-drive (and later 1/2-drive) socket sets in metal boxes, and for at least some of these sets, the sockets were typically stamped with five-pointed stars on either side of the size marking.

Currently we're uncertain about when this "Star" marking convention began, as we have examples of early sets (e.g. the Indestro No. 19 Socket Set and Indestro No. 28 Socket Set) in which the sockets were not marked with stars. For the sets with star markings, we have one reliably-dated set from 1931 to show that the convention was in use at that time, but the remaining examples can only be roughly placed in the late 1920s to early 1930s time frame.

The next several figures will show examples to explore the "Star" markings.

Fig. 47. Indestro 1/2-Hex Drive Sockets from No. 220 Set, ca. Late 1920s to Early 1930s.

Fig. 47 shows a group of sockets from an early 1/2-hex drive Indestro No. 220 Socket Set. The sockets are marked with the fractional sizes (in the style of "5-8" for "5/8"), and in addition have five-pointed star symbols on both sides of the size marking. This pattern has been observed on other examples of Indestro sockets, suggesting that the star symbols are intended as a specific mark for Indestro.

Fig. 48. Indestro 1/2-Drive 6-Point Sockets from 13-Piece Set, with Inset for Top View, ca. Late 1920s to Early 1930s.

Indestro's "Star" marking can also be seen on the 1/2-drive sockets from the late 1920s and early 1930s.

Fig. 48 shows the three largest sockets from an Indestro 1/2-Drive 13-piece Socket Set. The sizes are, from the left, 3/4, 25/32, and 13/16, and the finish is nickel plating.

Note again that the markings include five-pointed stars on either side of the fractional size, a feature also observed on the Indestro Socket Wrench shown elsewhere in this article.

The inset shows the interior of the 6-point sockets, illustrating the machined and cold-broached construction typical of that time.

The exact production date of this set is unknown, but it likely dates from the late 1920s to early 1930s.

Fig. 49. Indestro "Chromium Vanadium" 1/2-Drive Sockets with "Star" Marking, 1931.

Fig. 49 shows a group of sockets from an early 1/2-drive Indestro Chromium Vanadium 17-Piece Socket Set, dated to 1931 by a sales receipt. All of the sockets are marked "Chromium Vanadium" and have a five-pointed star on each side of the fractional size.

The sizes are, from the front left, 1/2, 9/16, 5/8, 21/32, and 11/16; and in the back row, 3/4, 13/16, 7/8, and 15/16. The inset at the top shows a typical "Chromium Vanadium" marking.

The sockets have a coarse knurled band around the base, probably intended to help with turning a loose nut by hand.

The fact that we have a reasonably precise production date for these sockets makes them significant in establishing a time frame for the use of the "Star" marking.

D-Trapezoid Marking on Duro Sockets

In our exploration of Duro Metal Products we often noticed a trapezoid symbol resembling a stylized "D" stamped on early Duro sockets. This stylized "D" symbol was assumed to be an identification mark for Duro, and this was finally confirmed by illustrations found in the 1935 and 1939 Duro catalogs.

Fig. 50. 1935 Catalog Listing for Duro Carbon-Steel Sockets.

Fig. 50 shows a scan from page 40 of the 1935 Duro catalog, and the illustration of "Case Hardened Special Steel Sockets" clearly shows two trapezoid symbols visible on either side of the size marking. We'll refer to this symbol in the text as the D-Trapezoid logo for ease of reference.

It's a little ironic to note that by the time of the 1935 catalog, Duro was probably no longer marking sockets with the trapezoid symbol — a least we've never seen an example of the later 12-point cylindrical sockets with a D-Trapezoid marking. We do have an example of a 6-point cylindrical socket with the marking, suggesting that the marking persisted until around 1933-1934.

Fig. 51. 1932 Catalog Listing for Duro Socket Set.

Fig. 51 shows an earlier catalog listing for a Duro socket set with the D-Trapezoid markings visible in the illustration, as found on page 72 of the 1932 J&R Motor Supply catalog.

This source is valuable as an example of how the socket sets were presented at the time when the D-Trapezoid marking was in active use. A careful look at the illustration shows that the 6-point sockets appear to have a cylindrical form in the larger sizes, instead of the fluted base found in earlier sets. This observation may be helpful in estimating production dates for socket sets.

Fig. 52. Duro 1/2-Hex Drive Sockets, ca. 1929-1930.

Fig. 52 shows two of the 1/2-hex drive hex sockets from the Duro LTX316 Socket Set, with sizes 3/8 and 7/16. (Note that the opening shown in the photograph is the 1/2-hex drive end.)

Most of the sockets in the LTX316 set are marked only with the fractional size, but several of them also have a distinctive trapezoid symbol resembling a stylized "D".

Fig. 53. Early Duro 1/2-Drive Sockets with D-Trapezoid Marking, ca. 1928-1931.

Fig. 53 shows a group of three 1/2-drive Duro sockets from a Duro No. 825 Socket Set believed to be representative of early Duro production. These are from a socket set that included a Duro Metal 672 ratchet marked "Patent Pending", apparently original with the set and implying production around 1928-1931.

The sockets in the photograph are, from the left, a 25/32 hex socket viewed from the service end, a 5/8 square socket viewed from the service end, and a 1/2 hex socket viewed from the drive end.

The sockets in this set are similar in construction to those in the early Indestro sets, but are marked with a D-Trapezoid logo on either side of the size, where Indestro sockets sometimes used a five-pointed star.

Fig. 54. Duro 1/2-Drive Large Sockets with D-Trapezoid Marking, ca. 1929-1931.

Fig. 54 shows the three largest sockets from the Duro "Double Guarantee" 1/2-Drive Socket Set, with sizes (from the left) 15/16, 31/32, and 1 inch. The sockets are stamped with the Duro D-Trapezoid logo on each side of the fractional size, except that the 1 inch socket has only one "D" logo.

The finish is nickel plating.

The larger sockets in the set (from 11/16 up) have a distinctive design with a reduced diameter at the 1/2-square drive end, a pattern mirroring the reduced diameter at the service end for the smaller sockets.

The sockets have a band of cross-hatched knurling at the service end, with the knurling coarse enough to assist with turning a nut by hand. The photograph shows some of the variations in the knurling pattern -- the left socket has a very fine rectilinear grid, and the middle socket has a more coarse diamond cross-hatch pattern. Most of the sockets have a medium-fine cross-hatch pattern similar to the right socket, but at least one socket in the set had no knurling at all, probably due to a production accident.

Fig. 55. Duro 1/2-Drive 31/32 6-Point Socket with D-Trapezoid Marking, with Inset for Top View, ca. 1932-1933.

Fig. 55 shows a Duro 1/2-drive 31/32 6-point socket with a cylindrical form, stamped with D-Trapezoid logos on each side of the fractional size.

The finish is cadmium plating.

This socket is believed to be representative of Duro's carbon-steel sockets around 1932-1933, after the cylindrical form had superseded the fluted base, but before the change to 12-point broachings.

Duro and Indestro socket sets often included specialty sockets with square studs in various sizes, intended primarily for removing drain plugs. These sockets were often unmarked except for the size, but are listed in the older catalogs with assigned model numbers.

Fig. 56. Duro [9954] 1/2 Inch Drain Plug Socket with D-Trapezoid Symbol.

The older Select Steel (carbon-manganese) socket sets included drain plug sockets with sizes ranging from 5/16 to 11/16, with corresponding model numbers 9951-9957 for Duro and 6651-6657 for Indestro.

Fig. 56 shows an example of the Duro [9954] socket, marked with the size (1/2) and the D-Trapezoid symbol. The corresponding Indestro pieces are essentially identical, except that they omit the D-Trapezoid marking.

The newer alloy steel socket sets also included drain plug sockets. Duro offered these in sizes from 5/16 to 3/4 by 16ths, plus the 11/32 and 13/32 (hexagon) sizes for Hudson-Essex applications. The model numbers were of the form "13xx" where "xx" is the size in 32nds.

Fig. 57. Indestro [3316] Chromium Vanadium 1/2 Inch Drain Plug Socket.

Indestro offered fewer sizes, just 5/16, 3/8, 7/16, and 1/2 with model numbers of the form "33xx" as above.

Fig. 57 shows an example, an Indestro [3316] 1/2 inch drain plug socket marked "Chromium Vanadium".

The D-I Socket Marking: Wartime Production

There is another socket marking that may be seen occasionally, but which doesn't correspond with any of the expected markings previously discussed. The sockets with this marking closely resemble the "Chromium Vanadium" or Indestro Super sockets, with knurled bases and tapered walls, but are marked with "D - I" instead of the expected Indestro brand.

Fig. 58. Sockets Marked "D - I" with 12xx Part Numbers.

Fig. 58 shows some examples of sockets with the "D - I" marking. The models and sizes are, from the left, 1228 (7/8), 1224 (3/4), and 1218 (9/16).

Numerous other examples have been found, in drive sizes from 1/4-drive up to 3/4-drive.

Based on the close physical resemblance of these sockets to the Indestro models, the "D - I" notation almost certainly denotes "Duro-Indestro". For example, one set of D-I sockets was acquired in a metal box with a Duro-Chrome sticker. In addition, the 1/2-drive D-I sockets usually have a standard Indestro 12xx part number (as in this figure), offering further evidence of the Duro/Indestro connection. But why would they have been marked differently?

Our first assumption was that these might be very early sockets, produced before the standard markings were developed. This fit nicely with the observation that all D-I sockets found thus far are either of unfinished steel or have a thin cadmium plating, rather than the polished chrome in use after the mid 1930s.

However, subsequent findings forced us to reject of this idea. One piece of contrary evidence is that all observed D-I sockets have been hot-broached, which based on the patent date pushes the production to post-1935. Also, the presence of the 12xx part numbers implies production in the late 1930s, at which time the standardized marking and polished chrome finishes would be expected.

Another possible explanation is that the D-I sockets were intended as an economy brand, made with cheaper steel and finishes. But if this were the case, they would have been given new part numbers — reusing the Indestro 12xx part numbers would be too confusing for customers.

After the above considerations, one explanation remains that appears to fit all of the observations: the D-I sockets represent wartime production, when rationing of key materials (including chromium and steel itself) forced companies to work with lesser quality steel, or at least forego polished chrome finishes. The D-I sockets might have been produced under a special contracts, as with the Plomb "Wright Field" WF-xxx series tools, or they might have been regular civilian production made to lower standards or with a plain finish. In either event, it would have been desirable to mark the items distinctly so that they wouldn't affect the reputation of the well-known Duro/Indestro brands.

Production Characteristics

In this section we'll look at some of the particular features of Duro/Indestro production that can help identify their tools. In general these production techniques would not be unique to one company, but when combined with other factors can help distinguish the maker of a tool.

Streamlined Panel Design

The importance of the 1937 "Streamlined" design trademark cannot be overestimated, as this greatly influenced the design of tools in subsequent years. In addition to the depressed panels on the Indestro "Select Steel" wrenches, box-end wrenches received dart-shaped raised panels. Even the designs for tools like pliers (e.g. the Duro 2114 Battery Pliers) sometimes incorporated a single dart.

Ersatz "Ultra-Box" Panels

Duro/Indestro were fiercely competitive and it seems that nothing provoked their competitive spirit like an opportunity to undercut Herbrand. When Herbrand came out with a new line of "Ultra-Box" wrenches around 1935, Duro/Indestro was right there with a knock-off of Herbrand's paneled design.

This first figure shows what Herbrand's design looked like — note that the left end of the parallelogram panel points up.

Fig. 59. Herbrand 3927 9/16x5/8 Offset Box-End Wrench, with Insets for Side View and Back Side Detail, ca. 1935-1940.

Fig. 59 shows a Herbrand 3927 9/16x5/8 offset box-end wrench with raised parallelogram panels, stamped "Van-Chrome" on the front panel, with the model number and "Made in U.S.A." on the back side panel.

The overall length is 8.5 inches, and the finish is chrome plating with polished faces and ends.

Then in this figure we see the Duro/Indestro version as made for Western Auto's ChromeXQuality brand. It looks quite similar, but the parallelogram has been flipped on its long axis so that the left end points down.

Fig. 60. ChromeXQuality 5/8x11/16 Offset Box-End Wrench, with Inset for Back Side Detail, ca. 1936-1939.

Fig. 60 shows a ChromeXQuality 5/8x11/16 offset box-end wrench with raised parallelogram panels, stamped with "ChromeXQuality" and the fractional sizes on the front panel, with "Chrome Vanadium Steel" in a slanted font on the back side.

The overall length is 10.0 inches, and the finish is chrome plating with polished ends and panels.

The wrench can be identified as Duro/Indestro production by the design of the box-end forgings and general construction, as well as the use of the slanted script for the "Chrome Vanadium Steel" mark.

This ersatz-Ultra-Box design was generally only used for ChromeXQuality production, but a few examples showed up later as part of the Duro/Indestro's wartime production.

Trimming Marks

Screw-Machine Sockets

Fig. 61. Broaching Detail for Early 1/2-Drive Indestro Sockets.

Fig. 61 shows a closeup of the socket construction. If you look carefully at the upper righthand socket, you can see a small burr left by the broaching, showing that the broaching came after the recess was machined. The centers of the flats also show tooling marks where the socket was drilled out prior to broaching.

The Development of Hot-Broached Sockets

In May of 1935 Duro filed for an important patent on their new hot-broaching method for making sockets, and the patent was issued as #2,027,922 in January, 1936. The patent document has an excellent discussion of the prior art (cold-broaching) and the advantages of hot-broaching, and is highly recommended for anyone interested in the how and why of such things. Among the advantages cited are the increased strength of the sockets, the smooth broach free of chatter marks, and the relieved lip at the drive end that allows for easier connection to a drive tool. (The patent even mentions the attractive "scalloped" appearance of the metal pushed ahead of the broach.)

Early Duro-Chrome 16xx-Series Sockets

Fig. 62. Early Duro-Chrome 1/2-Drive 16xx Hot-Broached Sockets, with Inset for Broaching, ca. 1935-1937.

Fig. 62 shows several early Duro-Chrome hot-broached sockets in the 1/2-drive 16xx series, with an inset at the top to illustrate the broaching details. The sockets are marked "Duro-Chrome" and have a cross-hatched band flush with the surface.

The models and sizes are, from the left, 1628 (7/8), 1630 (15/16), 1632 (1 In.), and 1634 (1-1/16).

A close look at the inset shows some degree of variation in the shelf left by the broaching; in particular, the rightmost socket has a wide shelf with nearly perpendicular scallops. This suggests that Duro was still experimenting with their process at this early stage. The third socket from the left (model 1632) most closely resembles the modern form.

The drive openings of these sockets have smooth walls without the recesses found on modern sockets, another indication of their early manufacturing date.

By fortunate circumstance, it turns out that the hot-broach patent helps to estimate the production date of the Indestro Chromium Vanadium Socket Set displayed on a previous page. On close inspection of the sockets in that set, it turned out that some were hot-broached, while others were of the older cold-broached construction. With the reasonable assumption that production would have quickly shifted to the new hot process, this suggests that the Chromium Vanadium socket set was probably made in the 1935-1936 time frame. The socket set thus gives us a valuable snapshot of the design and construction of sockets being produced at that time.

In particular, we see that the sockets have the tapered walls and knurled base of the later modern sockets, and that the sockets were being finished with a highly polished chrome plating. Part numbers were not yet being used at this time, though, as the sockets have only the size markings.