The new Alpha-Nock HPX features a Nock Retention Groove that snaps into the TriggerTech trigger box on the TRX 515 & TX 440, allowing you to 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. Nock Retention Groove snaps into trigger box, allowing you to hear and feel positive engagement Eliminates the fit disadvantages and string wear associated with snap-on nocks HP aluminum bushing for increased strength and accuracy Beep bowstring groove Large, smooth radius base Elongated ears Order today!