Rectus 21 coupler with 6mm barb. Fits into 5 or 6mm hose. This quick connect for Argon Welding gas uncouples in less than a second! Shuts off when disconnected saving costly Argon gas. Great time saver - no need to find a spanner to undo the gas line to or from your welder or regulator if you are packing up at the end of a long day or have to shift work areas. Fits into a REC21PG5/8UNF regulator/flowmeter outlet or a REC21PG6NIP hose plug.