Each Fit nock features ultra-strong, impact resistant, clear polycarbonate nock construction encapsulating the super-bright single LED that’s activated by a patented string-activated, piston-driven linear contact switch. Like all Nockturnal nocks, the Fit is guaranteed to reliably activate immediately when the string is released, and it can be switched off quickly and easily with the Nockturnal Nock Tool, a small screwdriver or most broadhead tips via an opening in the side of the nock. With well in excess of 20 hours of lithium battery life, each Nockturnal Fit weights approximately 25 grains.