Nockturnal brings their revolutionary lighted nocks to the next level with the Shift Nock series! They provide a vital indication of where your arrow hit the animal, and also aid in locating your arrow if you miss. They utilize the innovative string-activated, piston-driven contact linear switch, but also feature a thumb-activated switch that can be used to activate/deactivate the illumination. The internal LED and batteries are protected by an ultra-strong, impact resistant, polycarbonate casing, and are both waterproof and shock-proof. Includes 2 nocks per pack. Features: Super Strong Clear Polycarbonate ConstructionWaterproof and Shock ProofAvailable Colors: Red, Green, Red/Green StrobingFits X, H, S, and GT ArrowsH (white bushing) = Fits smaller diameter carbon .233 ID shaftsGT (black bushing) = Fits smaller diameter carbon .246 ID shaftsS (gray bushing) = Fits standard carbon .244 ID shaftsX (no bushing) = Fits smaller diameter carbon .204 ID shaftsEach nock in this package weighs approximately 25 grainsDelivers more than 20 hours of lithium-powered battery life2-Pack Nockturnal Shift Universal Red Lighted Nock 2pk NT-810