Advancing the lighted nock design by which all others are judged, Nockturnal Shift FIT Lighted Nocks take the simplicity and reliability of the world's most dependable and user-friendly lighted nock to an entirely new level. The patented, string-activated, piston-driven contact 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. With 20+ hours of battery life and a durable design, these Nocks are built to last and perform like none other. Constructed of an ultra-strong, impact-resistant polycarbonate casing that protects the super-bright LED, Shift Nocks deliver on what users have come to expect from Nockturnal lighted nocks. Super-strong clear polycarbonate construction String-activated LED illumination External on/off switch Over 20 hrs. of lithium-powered battery life 100% waterproof and shockproof Each Nock weighs approx. 25 grains Universal bushings fit arrow shafts (G/X/H/S)Bushings: 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