Features: - Designed to fit AX405 .166 Diameter Crossbolts - Crossbow String Activated - Injection Molded - Super bright LED - 20+ hours - Approx. Weight: 44 grains - The metal injection molded Lit lighted nock system creates an audible click when properly secured to the crossbows string. The super-bright LED system is initiated by the forward movement created by the strings forward movement to engage Nockturnals patented crossbow string-activated linear switch with piston-driven assembly. These lighted nocks are exceptionally reliable and do not require any specific tools to set up and come factory-installed in the shafts. Side illumination ports on the nocks body allow for additional light dispersion and increased tracking as the nock moves. With more than 20 hours of lithium-powered battery life the extended burn time grants plenty of opportunity for reuse and easy identification long after the shot.