Advancing the lighted nock design by which all others are judged, the Nockturnal Shift lighted nocks take the simplicity and reliability of the world's most dependable and user-friendly lighted nock to an entirely new level. Thanks to the external on/off switch the process of turning an ultra-bright, string activated Nockturnal lighted nock off has never been easier. Just slide the switch and the nock turns off. It's that simple! With 20+ hours of long-lasting battery life and a durable design these nocks are built to last and perform like no other. Constructed of an ultra-strong, impact resistant, polycarbonate casing that protects the super-bright LED lights, Shift nocks deliver on what users have come to expect from Nockturnal lighted nocks. The patented, string-activated, piston-driven contact linear switch triggers the nock to illuminate immediately when the string is released and can be quickly turned off with the external switch, a true evolution in the world's most reliable lighted nock system. Features: Super strong, clear polycarbonate construction. Waterproof and shock-proof. Fits X, H, S, and GT Arrows. H (white bushing) fits smaller diameter carbon .233 ID shafts. GT (black bushing) fits smaller diameter carbon .246 ID shafts. S (gray bushing) fits standard carbon .244 ID shafts. X (no bushing) fits smaller diameter carbon .204 ID shafts. Each nock weighs approximately 25 grains. Delivers more than 20 hours of lithium powered battery life. 2 per pack.