Nockturnal X-Bow/Half Lighted Nocks (Pack of 3), Moon Red 20 plus hours of battery life Fits arrows with inside diameter of 246 Piston driven contact switch ensures L.Fittedd. Illumination every time Waterproof and shock resistant design is second to none No assembly required 20 plus hours of battery life Fits arrows with Inside Diameter of .246 Piston driven contact switch ensures L.E.D. illumination every time Waterproof and shock resistant design is second to none No assembly required