Abstract: A drill chuck key includes a bevel gear that is connectable with a collar of a drill to tighten or loosen the jaws of the drill and a mechanism for operating that bevel gear as the key is moved. The mechanism permits the tightening or loosening operation to be carried out using the same movement of the key, and prevents over- or under- tightening of the drill jaws. One form of the mechanism includes a double pawl engaging ratchet wheels one of which has at least one trip dog thereon so that identical oscillating motion of the key will impart tightening to the drill jaws and can also loosen those jaws. Another form of the mechanism includes epicyclic gearing.