The Adjustable Wrench: One Tool for Every Nut

The handle 10 carries a head 11 with a fixed jaw 12. The jaw's inner face has angular braces 13 "to strengthen the same and also to conform to one side of a hexagonal nut"; "the main office, however, of the braces 13 is to strengthen the fixed jaw 12 since it is at this angle that the wrench jaw is weakest and most likely to break." The movable jaw 17 has an extension 16 sliding in a slot 14 and a larger opening 15, with a toothed rack 19 underneath driven by a worm 22 on a screw 25. The rack stops short, leaving a blank portion 23 that forms "a positive stop to the outward movement" so the jaw "cannot be run out of an engagement with the worm 22 and be lost". A coil spring 27 presses the worm to keep it under tension, and a bend 31 on the spring locks the screw 25 so turning the worm cannot unscrew it. The worm's edges are knurled for the fingers. A hammer face 32 sits on the underside of the head, and a hexagonal hole 31 at the handle's end is made to fit the most common nut, "for example, a one inch nut", so the wrench can be used on it without adjusting the jaws.

Clamp a hex bolt in the bench vise with a nut on it. Close the jaws until they just touch the flats, with no rock. Measure the opening with the caliper and count the turns of the worm from fully closed. With the protractor, mark how far the handle swings before it hits a block placed beside it. Turn the nut, lift the wrench off, flip it over and put it back: note the smallest swing that still gains a new pair of flats, and compare with the notebook. Pull the handle so the load goes into the **fixed** jaw first (the movable jaw on the side the nut is turning towards), then the other way. Watch the movable jaw: pulled the wrong way it opens slightly and the nut corners start to round.

**Karl Peterson** of Jamestown, New York, filed US 1,133,236 on 18 January 1915, assigned to the Crescent Tool Company; it was granted on 23 March 1915. Adjustable wrenches with sliding jaws were much older; his claims cover the worm on its screw with a spring that both tensions the worm and locks the screw. **Honest limits.** The patent gives no head angle and no tooth pitch; the notebook uses examples. Many open-ended spanners use about 15°, which is the angle the notebook shows is best.