Vertical Clamp with 0 – 9 inch clamping envelope and 4-1/2 inch throat. 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. By FAR our most popular clamp.