Alloy Artifacts

Exploring Ingenuity in Iron ...

Blackhawk 151 Drain Plug Wrench

Drain plugs for engine and transmission lubrication are often square rather than hex, and the size and configuration (male/female) of the plugs varies widely among manufacturers. Some tool makers responded by creating special-purpose wrenches having multiple square or double-square openings, in the hope that one would fit whatever plug size was at hand.

Blackhawk had a different idea though (they often had different ideas) -- instead of offering a wrench with multiple fixed openings, they created a drain-plug wrench with multiple adjustable openings. In this way the wrench would serve not only for the sizes in use today, but for whatever future sizes were produced. The result was the model 151 drain plug wrench shown in the figure below.

Blackhawk 151 Drain Plug Wrench, with Inset for Markings, 1941. (Click for details and operation.)

The wrench offered four head positions designed to handle a wide range of square plugs, both male and female, plus one broaching to handle a male hex plug. In operation, the knurled collar was turned to adjust the chosen opening for the particular plug. The catalog specified the operational size ranges as 3/16 to 1-1/4 inch for male square plugs, 5/16 to 1 inch for female square plugs, and 7/16 to 1-1/2 inch for male hex plugs.

The handle of the wrench has raised ribs along the axis, a style used in the early 1940s, and shows a "-1" date code; according to our recently decoded interpretation of the date codes, this places the production in 1941. (See our discussion of Blackhawk date codes for more information.)

The 1953 Blackhawk catalog shows that the model 151 drain plug wrench was still in production then, at a suggested price of $6.07 net.