Abstract: A shaft assembly (11) having a spline (16) with an anti-backlash device operable due to centrifugal force to engage both sides of internal spline teeth during rotation. The spline (16) includes a main force transmitting portion (18) and a moveable spline sleeve (22) which during operation engages the side of teeth opposite the side engaged by the main force transmitting spline. Spline sleeve (22) rides on helix member to move slightly circumferentially as it is moved axially by a centrifugal force actuated member. A bar which is pinned to the spline (16) has one end which moves radially outward due to centrifugal force as the spline (16) is rotated and another end which engages and moves the spline sleeve (22) axially. When the spline sleeve (22) is moved, the splined end on the shaft assembly (11) is locked or wedged into engagement with the mating internal spline (14).