Releasable means for locking a shaft in an opening in a body, which opening is bounded by a peripheral, usually cylindrical, wall. A recess is formed in the wall and bounded at least in part by a circumferentially extending ramp-like bottom surface that extends for less than the full periphery of the wall, and a catch surface adjacent to the bottom surface. The catch surface extends radially. In the wall of the shaft there is provided a locking member which is resiliently biased to extend beyond its periphery and which can be retracted entirely within the periphery of the shaft. The lock member is restrained against rotation relative to the shaft so that when the shaft is pressed into the hole, the lock member can snap outwardly into the recess, thereby to lock the shaft in place, but the shaft can be released by twisting it so that the lock member is cammed inwardly to the diameter of the wall in which the recess is formed, and the shaft can thereafter be withdrawn.