This little brass adapter allows standard RV pigtails (black rubber or stainless overbraid) to be threaded into an RV regulator.
They come standard on two-tank automatic changeover regulators, but for some reason they are not included with one-tank regulators. If you plan to use a pigtail with your one-tank regulator, you need this.
The 1/4" male NTP end of this adapter threads into the regulator. The other end is a 1/4" female inverted flare. That's what the pigtail needs to make a connection. Please use a bit of gas-rated thread tape on between this and the regulator (but not on the flare end).