PROTO Adjustable Wrench: Alloy Steel, Black Oxide, 10 1/8 in Overall Lg, 1 3/8 in Jaw Capacity, Std

These automatic locking adjustable wrenches have a screw mechanism at the bottom of the head that adjusts the jaw size to ensure a tight grip on the fastener. Once the jaws are tightly adjusted, they automatically lock on the fastener head.