Designed to be used with most shallow engagement type release: Cobra, Scott, HHA, Fletchunter and other caliper releases. The Ultra-Nok stops the arrow from falling off the string at full draw. Designed to eliminate string wear, arrow pinching, and cable interference, it securely clamps to the string. Maintains positive peep alignment. Works well with conventional nocks 21/64 and smaller, Beman and Super Nocks.