Customize your own jigs. The T-heads fit inside T-slot track or a groove routed with T-slot bit #26099.Available in 5/16"-18 thread or 1/4"-20 thread.5/16" - 18 bolt bottom plates are 9/16"W x 7/8"L x 7/64"H. 1/4" - 20 bolt bottom plates are 9/16"W x 11/16"L x 7/64"H. Zinc-plated steel.Sold in packs of five.