Nockturnal-X Red Nocks require no assembly, they can go straight from the package to the arrow. The piston driven contact switch ensures L.E.D. illumination every time. Provides a water proof and shock resistant design. Offers 20 plus hours of battery life for many hours of use. Fits arrows with an inside diameter of 0.204. Comes in packs of 3. Piston driven contact switch 3 lighted nocks per pack 20+ hours of battery life No prep work needed Waterproof and shock resistant design Fits arrows with an inside diameter of 0.204