A locking device serving as a key for securing an annular member or hub against axial movement on a shaft and for repetitively self-returning the hub to an angular preset condition and thereafter holding the same against rotation relative to the shaft. The hub has a tapped radial hole through the center of which a transverse slot extends and in which the locking key is received. A set screw is threadedly advanced in the tapped hole to apply increasing pressure on the midportion of the locking key so that spaced parts of the key will contact the slot floor and a flat surface on the shaft creating moments of force which act in offset relation to the shaft''s axis with the result that relative rotation of the shaft and hub will occur until a preset angular or home position is reached at which time the slot floor and the flat of the shaft extend parallel to one another.