Simply remove the old nipple, Clean the threads and flame holes in the breech plug thoroughly, use some kind of anti-seize on the threads of the nipple, screw it back in and snug it up well. seat the cap on the nipple fully cock the rifle and pull the trigger. When it fires the gasses escape slightly from the hole in the side of the nipple, thereby releasing the cap so that when you pull the hammer back to remove the old cap it comes off very easily. Best nipples that I have ever used.