thoroughbrace

noun

1. (dated, historical)A leather strap supporting the body of a coach or wagon, attached to springs or serving as a spring itself.

   “Spring, tire, axle, and linchpin too, Steel of the finest, bright and blue; Thoroughbrace bison-skin, thick and wide; Boot, top, dasher, from tough old hide Found in the pit when the tanner died.”

   “The wagon-bed is supported by iron bands or perpendiculars abutting upon wooden rockers, which rest on strong leather thoroughbraces: these are found to break the jolt better than the best steel springs, which, moreover, when injured, can not readily be repaired.”

   “"Why, it happened by trying to make one coach carry three days' mail—that's how it happened," said he. "And right here is the very direction which is wrote on all the newspaper-bags which was to be put out for the Injuns for to keep 'em quiet. It's most uncommon lucky, becuz it's so nation dark I should 'a' gone by unbeknowns if that air thoroughbrace hadn't broke."”