This brass C02 nipple screws into a left hand thread gas inlet port on a brass regulator body. Includes a sealing quad ring, so you do not have to buy C02 sealing washers for sealing your C02 tank to your regulator. Does not include needed C02 nut, order item D39 separately. 2 5/8" long, with a 5/16" hex key port for installation and tightening. Also has an 11/16" nut on the end for installation and tightening. Remember, these left hand thread parts can be put in with threadlocker and other sealants, so they can be hard to remove.