Abstract: An adjustable, self-locking crow foot wrench comprises a support member having a pair of movable jaws. A worm adjustment member is rotatably journaled on the support member and engages rack teeth on the jaws to adjust their spacing for different size bolts. A locking element, guided for movement between the worm adjustment member and a drive-stud-receiving recess, is movable into locking engagement with the worm adjustment member in response to insertion of a drive stud into the recess. A spring moves it out of locking engagement in response to removal of the drive stud. In a two-piece embodiment, the support member is a portion of one of the jaws; in a three-piece embodiment, it is a third part.