You will receive a set of alloy cylinder connectors for homebrewing, including extra food grade rubber rings for better sealing and replacement when original rings age Our alloy CO2 cylinder adapter ensures secure, leak frees connection during carbonation The adapter connects to standard CGA320 CO2 tanks to refill TR21 4 threaded CO2 cylinders Made from alloy with electroplated surfaces, this adapter used in resistance, leak proof, high temperature durability, and low permeability for safe, efficient CO2 transfers The CO2 refill adapter features easy installation and simple operations Follow step by step diagrams to connects tanks and cylinders, filling slowly to avoid triggering connectors