Groovy T-Bone Top OnlyReplaces the cross bar of your Groovy T bone, or use the 4 way gear grooves for other applications. The Boonedox Groovy T Bone Top Only is a replacement for the Boonedox Groovy T Bone Truck Bed Extender system. It consists of the 50" anodized aluminum crossbar and integrated gear tracks, designed to be mounted above the truck bed, extending the cargo area by 48 inches. This setup is ideal for transporting kayaks, canoes, lumber, and other long items