Unlike the standard Leatherman pliers, the locking will snap to a constant tight grip, similar to Vice Grip tools. They also are slightly curved.
Use the screw knob on the rear of the tool to adjust the jaw opening. Set it to be slightly smaller than the width that you want to grip. Then place the jaws around the object, and clamp down. You may need to tweak the screw to get the desired clamping force.