The NEW Alpha-Nock HPX features a Nock Retention Groove that snaps into the TriggerTech trigger box on the TRX 515 & TX 440 allowing the user to both hear & feel the positive engagement of the nock to the string indicating your arrow is properly locked & loaded in the crossbow. In addition the snap-in design of the Nock Retention Groove eliminates the fit disadvantages & string wear associated with snap-on nock designs. – The Alpha-Nock HPX also features an HP Aluminum Bushing for increased strength and accuracy a deep bowstring groove a large smooth radius base and elongated ears. The crossbow string wraps tightly around the center of the Alpha-Nock HPX resulting in straight nock travel and precision down-range accuracy while minimizing serving wear.