UFA's (Universal Fill Adapters) are often components of a CO2 fill station or remote line.  They have a female ASA port on the bottom that you can screw your tank in to and a female 1/8" NPT port on the side to connect to the remote line or fill station line.

Ninja Tech Notes: This UFS is non-rebuildable so do NOT try to crank off the knob with a wrench.  However, because of the design there is no air passing arround the internal oring and the oring isn't travling over any vent whole that would cause catching or tearing.  So each time you use this just put a drop of paintball gun oil on the knob threads at the top and a drop on the pin depressor from the bottom and it should last a long time.  This is the same UFA we use at our paintball park for doing lots and lots of fills.