Abstract: A drill chuck has clamping jaws which can be locked by means of the thread on a chuck member. The thread has a small pitch. The clamping jaws are positioned by a guide sleeve. An adjustment adapter positions the guide sleeve and adjusts the clamping jaws via a coupling member selectively engageable with the thread. The coupling member has threaded segments selectively engageable with the threads on the chuck member. The coupling member is engaged with or disengaged from the chuck member by rotation of the adjustment adapter relative to the coupling member. Cams on the adjustment adapter co-act with control faces on the coupling member in selectively positioning the threaded segments. With the threaded segments disengaged, the adapter moves the guide sleeve into the desired position to clamp the jaws on a drilling tool or bit and the jaws can be locked by engagement of the threaded segments with the thread on the chuck member.