This 20mm post and clamping knob are used in combination with a mounting plate (available separately). Attached to the bottom of a Kreg hold-down clamp, they let you quickly position the clamp anywhere in the perforated table top of a Festool MFT/3 multifunction table. The post is 11/16" long – just less than the table top’s 3/4" thickness – threaded internally for use with the supplied clamping knob (or an MFT accessory clamping knob). The steel post has barb-like ridges along its length to prevent upward movement when clamping force is applied.