Locking Pliers: A Grip That Holds Itself

Petersen's handle A is "of channel formation" with its outer end closed, and a shank 3 threaded through that end with a head 4 for turning it and a point 5 inside. The stationary jaw 6 at the other end has its working face at "approximately 22½ degrees" to the handle. The movable jaw 10 pivots on a pin 8. Section 11 of the articulated lever pivots on the movable jaw and is "extended to provide an operating handle 14"; section 12 reaches into the handle, where a pocket 16 in its end receives the point 5 of the shank. Pressing the lever forces the movable jaw toward the stationary one. A coil spring 15 opens the jaw again, "so that my improved tool may be employed with substantially the same convenience and the effectiveness as a ratchet wrench." Turning the shank moves the lever's fulcrum and so sets the jaw opening. The patent says the tool "can be engaged with the work with the grip of a vise and particularly when the operating handle 14 has been swung outward and the handle A is beyond center and the shank 3 adjusted to further force the jaw 10 into engagement with the work". It is meant to serve as pliers, ratchet wrench and pipe wrench.

Close locking pliers on a hex nut threaded onto a bolt in the bench vise. Turn the adjusting screw until the handles just close with a firm snap, and lock them. Let go: the pliers stay on. Hook the spring scale to the handle end and pull square to it until the nut turns; record the reading. Give the screw a quarter turn tighter, lock again, and repeat. Watch the handle as it snaps over: feel the force rise to a peak as the links straighten and fall as they pass it. Release with the release lever (modern pliers) and look inside the handle: find the two links, the screw's point and the spring, and match them to Petersen's 11, 12, 3 and 15.

**William Petersen** filed US 1,489,458 on 5 January 1923 and it was granted on 8 April 1924, half assigned to Jules A. Bibe of De Witt. He had filed an earlier wrench patent, US 1,392,443, granted 4 October 1921. Later locking pliers added a release lever. **Honest limits.** The link-force formula ignores friction and assumes rigid links; the stiffness and screw pitch in the notebook are examples, not Petersen's figures.