|The best part of holdfasts is how fast they work. You hit them on the top of the arm to lock them and on the side of the stem to loosen. In general they are used (and work even better) in pairs.
The holdfast is designed for 3/4" hole in a workbench top of a 1 3/4" thick or thicker. 6 1/2" reach. Maximum clamping 7 1/4" in a 2" thick benchtop. Patented. Made in USA.