A drill chuck has a chuck body, a holder body, and a front sleeve surrounding the bodies, with jaws between them. A ring of teeth on one of the bodies can be engaged by a pawl angularly fixed on the other of the bodies. When engaged, the pawl and the array of teeth allow rotate relative to the chuck body in a tightening direction but not in a loosening direction. Respective interengaging stops on the other body and on the front sleeve limit relative angular movement of the front sleeve on the other body between a pair of angularly offset end positions. A back control sleeve has a cam formation engageable with the pawl in only one of the end positions to hold the pawl in the freeing position. The pawl is biased by a spring in the other end position into the locking position.