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America on the Move
Collection Exhibition Themes
Monkey Wrench
Catalog #: 2002.0075.11, Accession #: 2002.0075
Currently on display
From the Smithsonian Collection
This heavy wrench was used in steam locomotive and railroad-car repair work.
Physical Description
Wrench with threaded adjusting screw. 3" W x 12" L
Date Made:
Dates Used:
1850s - Today
Type wrench used everywhere, all trades
Gift of National Park Service

Part of a small array of hand tools displayed in "America On The Move" - such tools were used in the inspection and repair of steam locomotives. Light repairs on steam locomotives were usually done in roundhouses at the many small locomotive terminals throughout a railroad's system; heavy repairs were done in a large, centralized repair shop serving the whole system (often referred to as the "Back Shop"). Most of these tools date from the early- to the mid-20th century, roughly 1900-1955.

The term "monkey" wrench may have come from the lowly place in the shop-tool hierarchy that a monkey wrench occupied: a skilled mechanic used a monkey wrench only when a solid, open-end wrench was not available to properly fit a bolt or nut in question, or when the head of the bolt or size of the nut was non-standard. The jaws of a monkey wrench were only grossly adjustable (unlike the fine adjustment on a modern crescent wrench) and usually made a poor or loose fit on the nut or bolt head. "Monkeying" off a nut or bolt with such a wrench often involved several tries to get the wrench to fit without its slipping off.

Also, the shape of the head lent itself to be using impromptu as a hammer, which of course damaged the wrench, causing the adjustment of its jaws to become even looser.

If a wrench slipped off a nut or bolt head - as monkey wrenches were prone to do - injury to the user was often the result.

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