The frame (5) is coupled to gripper rings (3) and is securable at the barrel edge by at least three clamping claws. A movable claw (7) is provided which is radially clampable by a clamping device (9) contg. a clamping lever (10) swivelably mounted on the frame. The lever is coupled to the movable claw, radially displaceable on the frame via puller (14). Pref. the clamping lever lies between the gripper ring and the frame inside the region surrounded by the gripper ring. The lever may be assertible on the frame in its clamping position.
