The Nockturnal lighted UNISIZE Nocks are sized perfectly to fit directly into the Nock On Series 5mm Arrows. They also have universal bushing to fit S H and GT size arrows. These nocks are an ideal nock fit on the string compared to the standard X nocks and fly amazing. Amazingly bright with a super long battery life. – Nockturnal Lighted FIT Nock – Features: – Super Strong Clear Polycarbonate Construction – Fits X H S and GT Arrows – 20+ Hour Battery Life – 3-Pack – Improved LED’s in your Green Strobing nocks – Non-Strobing FIT Nock: Designed to fit nearly every hunting arrow on the market the Nockturnal Fit non-strobing base nock will fit X-diameter arrows and each three-pack of Fit nocks includes three sets of Nock Collar adapter sleeves to fit GT S and H arrows. 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 newly designed 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 and will remain brightly lit for arrow retrieval and can be easily spotted in daylight or darkness.