NuFletch Ignitor Lighted Nocks for Vertical BowsNuFletch Ignitor Lighted Nocks for Vertical Bows Install the correct insert for your arrow into the back of the arrow Place the LED in nock and slide into the insert Ignitor contains 3 complete lighted nocks that fit the 4 most common nock sizes (GT, S, H, and X) inside diameters LED's are removable and replaceable Save battery life by practicing without the LED in Green LED provides up to 50 hours of continuous light