The Nockturnal S Lighted Nocks feature a string-activated linear switch located deep inside the nock, so it can't fail. Clear plastic for super visibilitycan be seen hundreds of yards away. Weighs 25-50% less than other lighted nocks. Nockturnal S models fit most standard arrows. String-activated linear switch is located deep inside the nock Clear plastic for super visibility Can be seen hundreds of yards away Weighs 25-50% less than other lighted nocks Nockturnal S models fit most standard arrows