The keg coupler connects to the keg valve, "tapping" the keg. Both the gas line from the CO2 tank / regulator and the beer hose to the beer faucet attach to the coupler.

Used by but not limited to the following brewerys:  Guinness Stout, Harps, Kilkennys, and Smithwicks Irish Ale.
 

Beer Keg Tap Features:

• Well-type connection
• Stainless steel probe
• Easy to engage handle: push down to tap/pull up to untap