The WSC-16134 Weldsale 9″ Fast Action Vertical Clamp is our standard clamp. It has a 9″ envelope and a 4 1/2″ throat. It uses our knurled boot which is designed to effortlessly drop into the hole and grip effortlessly. Simply drop the Round Knurled boot into a Weldsale 1-3/4″ square hole, tilt the clamp back, slide the arm down until the swivel pads contacts your work piece, and turn the screw. This is a very simple, fast, and strong clamp. It clamps and unclamps in seconds!