Monkey (railroad) wrench

This heavy wrench was used in steam locomotive and railroad-car repair work. 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 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. This tool is part of a collection of hand tools used in the inspection and repair of steam locomotives in the early- to the mid-20th century, roughly 1900-1955. 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").