Twist a set screw to tighten or loosen these clamps, or connect them to hydraulic pressure to automate the movement. As you tighten these clamps, a serrated jaw pushes in and down against the side of your workpiece, holding it in place. To switch from manual to hydraulic clamping, remove the set screw and swap in a cylinder and tube end cap (sold separately), then connect your hydraulic line. These clamps have more holding force and a larger clamping stroke when used manually. Secure them to your machine table with two bolts (not included).