This 14-gage stainless steel part made by MAR-K 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 sides 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. Part is covered with plastic film to protect the stainless surface. This will need to be removed before installation. Part is approximately 2-1/8 inches tall. Made in Oklahoma City, USA.