Trying to find your arrow after shooting through or into a big game animal in low light just became a lot simpler, thanks to the Nockturnal Lighted Nock. Nockturnals replace your standard nocks, and they light up after they're shot from your bow. Take a knife blade or other object, and turn off the light after you recover your arrow. A breakthrough design that is more affordable and lighter than most lighted nocks String activated linear switch that is protected deep within the nock and will not turn on or off inadvertently Made of clear plastic for maximum light transmission Battery lasts over 20 hours Weighs approximately 20 grains Size: .204" for 5MM X series shafts