PROTO Adjustable Wrench: Alloy Steel, Black Oxide, 8 5/32 in Overall Lg, 1 7/32 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.