1958-1959 Rear Cross Sill (Fleetside) -GM Truck These is for trucks equipped with wood bed floors only. This 14 gauge steel cross sill is mounted across the frame under the wood for support. Bolt holes in the cross sill determine the placement of the bed strips and wood. The bed strips and bed side angles are bolted to the cross sill and the wood is bolted to the frame through the cross sill by the bed-to-frame bolts. Cross sill is sold with holes and includes brackets. Made in USA!