Abstract: The proposed chain tightener is provided with a damping piston (3) in a guide bore (2). A stop ring (8) is provided between the damping piston (3) and the housing (1). The stop ring (8) cooperates with grooves (9, 17, 13) and stops (11, 10, 14) on the housing (1) and on the damping piston (3), preventing the damping piston (3) from sliding too far into the housing (1). To allow the damping piston (3) to be locked in position in the bore (2), it is proposed that the stop ring (8) should be clamped in a locking position between two contact surfaces (12, 16) on the housing (1) and damping piston (3) respectively, the contact surfaces (12, 16) being inclined in relation to the axis of the damping piston.