TenPoint Alpha Nock HPX Yellow 12 pk. TenPoint Alpha Nock HPX;Pack of 12;Mandatory for use with TenPoint rail-less crossbow models TRX 515 and TX 440;Features a Nock Retention Groove for secure engagement with the TriggerTech trigger box, providing auditory and tactile confirmation;The "snap-in" design of the Nock Retention Groove enhances fit and reduces string wear compared to "snap-on" designs;Constructed with an HP Aluminum Bushing for improved strength and accuracy;Designed with a deep bowstring groove, a large smooth radius base, and elongated ears for straight nock travel and precise accuracy while minimizing serving wear