A keyless chuck includes a jaw housing with jaws that are advanced in respective guideways to grip a tool bit and retracted to loosen the grip on the tool bit. A jaw thrust member is coupled to the jaws and to a threaded spindle and is forced forwardly or rearwardly to advance or retract the jaws. The threaded chuck spindle engages the jaw thrust member through a small-area contact patch to limit the operating friction and thus provide a chuck which can be readily hand-tightened and which self-tightens in response to torque transmitted through the chuck. A lock mechanism is provided to selectively lock a chuck adjusting sleeve relative to the jaw housing to allow uni-directional movement of the chuck adjusting sleeve relative to the jaw housing or selective bi-directional locking of the chuck adjusting sleeve relative to the jaw housing. The lock mechanism includes a lock plate coupled to a chuck adjusting sleeve and includes a set of teeth on an axial face for engagement with complementary teeth on an axial face of the chuck adjusting nut. The lock plate is normally spring-biased into engagement with the chuck adjusting nut and can be disengaged from the chuck adjusting nut to temporarily disable the locking mechanism. The keyless chuck is assembled in such a way that the run-out of the finished chuck is minimal.