Automatical X Lighted Nocks for Arrows Lighted Nocks feature a string-activated linear switch located deep inside the nock, so it can't fail. Clear plastic for super visibility- can be seen hundreds of yards away. Weights 25-50% less than other lighted nocks. X models fits for inside diamter 0.204 inch( 5.3mm) arrows, Method of use: The nock will be lighted by the pressure of tense string. you can use a little tool to push the colorfull part up through the hole when you want to colse the lighted led.very easy and convenient to use.