Abstract: A spindle assembly has inner and outer coaxial shafts having front and rear ends and extending along a common axis with the inner shaft axially displaceable in the outer shaft, a holding assembly on the front ends adapted to grip a tool or workpiece in an axially forwardly displaced position of the inner shaft relative to the outer shaft, a coupling ring fixed on the rear end of the outer shaft, and an actuator having a piston axially engageable with the rear end of the inner shaft and operable to axially shift the inner shaft in the outer shaft. In accordance with the invention complementarily interengaging formations on the actuator and the coupling ring including a groove and a projection are displaceable between a holding position axially securing the ring on the actuator and a freeing position allowing the ring to be axially separated from the actuator.