An apparatus is disclosed for releasably holding a toolholder shank having a lockable surface and a releasable surface utilizing an actuating bolt with an associated threaded actuating nut. When the actuating bolt is rotated in a locking direction, the actuating nut is drawn onto the bolt thereby clamping against the lockable surfaces of the toolholder shank. When the actuating bolt is rotated in the releasing direction, a releasing segment acts upon the toolholder thereby ejecting it from the tool support member.