Nockturnal Predator Crossbow nocks are piston driven contact switch ensures L.E.D. illumination every time. Waterproof and shock resistant design is second to none. Nocks can go straight form the package to the shaft in fully operational condition. No prep work needed. Just insert it, and you are ready to shoot. Shoot it at dusk, and with over 20 hours of battery life, you can still find your arrow the next day. There are 3 Green Nocks per pack and fit all bolts in the size 1 category.