Bright Lumenok light comes on when arrow is released, then stays on until you turn it off. Gives you a good look at your arrow flight, from release to impact. Plus, Lumenock nocks make it easy to find missed shots. Easy to install…simply remove your nock and install the Lumenok. When the nock is fully seated against the electrically conductive end of the carbon or aluminum arrow shaft, the Lumenok lights up and is ready for action. Wiggling the nock in the shaft breaks electrical connection between the arrow shaft and the Lumenok, causing the light to go off. Lightweight... adds only 22 grains of weight to arrow; Works with any aluminum arrow with Super Uni bushing and most popular brands of carbon arrows; 3V lithium batteries have 5-year shelf life, stay lit continuously for 40 hrs.; Fits .245" ID carbon and aluminum shafts; Uni-nock design; 2 1/2" long; Red; GT nocks; Mfg. Number: SL-3; Order now! Lumenok Lighted Arrow Nocks, 3 Pack