And the Artifact is . . .

 . . . a wagon jack, pictured here in front of the buggy near the Chesebro blacksmith shop in our Prairie Stories exhibit!  Well done, Jess C., who posted her guess in our Facebook comments!

Wooden wagon and buggy wheels would be "ironed" by placing an iron rim around the wheels to protect them from bumps in the rough roads.  Blacksmiths would weld two strips of iron together which were bent to match the exact size of the wooden wheel rim.   Fitting the iron rim onto the wood was an exacting process requiring the metal be heated to a precise temperature--too hot could burn the wooden wheel, but too cool could result in a poor fit.  If the blacksmith was skilled, the cold water poured over the hot iron rim would cause the metal to shrink to a close fit.  Wagon jacks were often built by the same blacksmith who had ironed the wheels, and prudent travelers of the era would never travel without one.  Often wagon jacks were carried on the back of the wagon, near a grease or tar bucket containing lubricant for the axles.