Abstract: A ball cage for a helical ballspline of a mechanical movement device comprises a cage in the form of a tubular sleeve adapted to be arranged between a helically threaded inner member and a complimentary helically threaded outer member of the helical ballspline. The inner and outer members are displaceable relative to one another along a helical path formed by the threads thereof. The tubular sleeve of the ball cage includes a plurality of ball pockets formed therein for accommodating thrust transmitting balls of the ballspline arranged in the helical path.