The Trak Clamp works with the Mini Trak, Top Trak and Heavy Duty Trak to hold your work to the workbench. The clamps hold best when used in pairs. Be sure you have the base of the clamp seated in the Trak so that you don't pull the tack out of the work surface! Bolt is 1/4"-20 thread. Drill a 1/4" hole with a 7/16" countersink for the bolt head.