A heavy wooden or metal crossbeam resting on the front axle of a horse-drawn wagon or vintage trailer. It supports the bed of the wagon while elevating it enough to give the front wheels clearance to pivot during tight turns. Without this spacer, the wheels would rub against the underside of the bed and restrict the turning radius.
Heard on the job
The old hay wagon needs a new bolster fabricated before we can safely load it up again.