"Never lose a small-diameter hunting arrow again with the bright, easy-to-see performance of the Burt Coyote Lumenok X Lighted Nock! Designed for use with high-performance .204""/5mm I.D. hunting arrows, these lighted nocks replace your standard original internal mount nocks. Lights up automatically when seated against a carbon or aluminum arrow shaft to help you see the arrow's path and final resting spot. Stays lit for up to 40 hours. No magnets, no glue, no switches or moving parts. Light can be disengaged by backing nock out of arrow shaft. Lighted replacement nock for high performance, small-diameter hunting arrows Fits .204""/5mm I.D. hunting arrows Lights up automatically when shot Stays lit for up to 40 hours No magnets, glue, switches or moving parts"