Commonly referred to as the "Twist On Coupler"Suitable for attaching Asahi, Heineken, Hofbrau KegsIncludes:1 x – S-Type Coupler with 5/8" Male Beer and Gas threads2 x – duotight 5/8" duotight to 8mm push in1 x – Non-Return Ball or Torpedo check piece (Non-Return Liquid)1 x – Gas Duck Bill valve (Non-Return Gas)How to install Gas Duck Bill ValveRemove black EPDM washer inside 1 of the duotight push in fittings that you will use for gas. The duck bill valve is a washer as well as a non-return check piece.It is optional, you do not have to use the non-return check pieces for gas or liquid.