With no-fail internal components and bowstring activated dependability, Halo Lighted Nocks provides superior, dependable performance with every shot. Sold in a 3 Pack. Size Guide Micro - Fits micro arrow IDs of .165"-.166" Halo Nocks provides superior, dependable performance with every shot. Their patented design wont accidentally turn on when placing on your bowstring. No matter how hard you push on the nock, it won t activate until it leaves the string. In addition, this innovative design avoids any risk of a mini-dry fire that can occur with other lighted nocks that slip forward during release. The Halo Nock is refreshingly simple to use and available in a variety of colors and sizes.