Abstract: A key device for locking an element to a shaft for rotation therewith includes a key-engaging surface on the shaft which is provided with first and second opposite ends and angles radially inwardly toward the shaft axis. The first end of the key-engaging surface is located at the shaft periphery, and the shaft is provided with a radially extending shoulder at the second end of the key-engaging surface. An element to be secured to the shaft has a shaft-receiving opening which receives that portion of the shaft having the key-engaging surface. The element is provided with an outer side and a radially extending keyway which opens through the shaft-receiving opening in registry with the key-receiving surface. The keyway is provided with a rear cam surface which extends angularly from the outer side of said element at a point radially spaced outwardly from the shaft-receiving opening to the shoulder on the shaft.