Lighted nock that is activated by the force applied to it upon the release of the arrow and deactivated by slightly pulling it back as to break the contact. Designed to aid in watching your arrow flight and recovery of you game. Five sizes to fit most carbon and aluminum shafts. Available in nock sizes, X,H,S,GT,and F sizes. Available in single or three pack.Weighs approx.25 grains each.