This homemade spanner was used in steam locomotive repair work to tighten/remove very large, critical bolts. The wrench would need to be used with a very long 'extender' on the handle to gain the necessary leverage. The spanner was used on bolt heads and nuts that hold the front-end (or the "smokebox" portion) of a steam locomotive boiler onto the cast-steel "saddle" that is the foundation of a steam locomotive's cylinder-and-mainframe assembly. The strength and tightness of these "saddle bolts" that join boiler and saddle are crucial to keeping the locomotive from literally shaking itself apart when underway down the track. This crude spanner was likely home-made in a roundhouse far from a full repair shop.
