Abstract: An assembly positionable on the spindle of a machine tool for securing a workholding apparatus in position on the machine tool. The assembly comprises first and second end portions and an inner piston axially movable within an inner chamber formed by the first and second end portions when assembled together. The piston, first end portion and second end all comprise central openings which permit the draw bar of a workholding apparatus to pass therethrough and into engagement with a draw rod of a machine tool. The piston includes springs, to urge it in a retracting direction, and spaced apart lugs to engage similar lugs on the workholding apparatus for securing the workholding apparatus to the assembly and thus to the spindle. Retraction of the draw rod results in the springs urging the piston, and hence the lugs of the workholding apparatus, in the retracting direction to secure the workholding apparatus to the assembly.