Positioning rings GN 9192.2 limit the swiveling range of down-thrust clamps GN 9192 to 110° left or right via a positioning pin. The position of the ring can be adjusted to ensure that the clamping position is reached reliably when the clamp swivels against the positioning pin. The positioning ring is secured with two set screws. The stroke of the down-thrust clamp is reduced by the height h1 of the positioning ring.