Description: High-Visibility LED HIGH VISIBILITY and LONG LASTING LITHIUM BATTERIES - Shoot it at dusk, and with 20+ hours of battery life, you can still find your arrow the next day fits for compound bow and recurve bow bolt size 0.165"(4.2mm) ID FITS ARROWS WITH INSIDE DIAMETER .165 - Including Victory-VAP Armor Piercing, Easton A/C/C and G-UNI Method of use: NO ASSEMBLY REQUIRED, there is switch on the nock, this nock is string-activated type nock, it can be lighted by the pressure of string, if you want the light on before shooting, just push the switch down, if you want the light off, then push the switch up, very easy and convenient. Attention: if the nock can't lighted up by the pressure of string, please try to push the colorful switch on the nock.