This is a brass CGA 1340 tube trailer connection for inert gases.  The nut has a 1-11.5 NPS RH thread and the tailpiece is 1/2" MNPT. This CGA 1340 brass connection is manufactured in accordance with the Compressed Gas Association V-10 standard. This connection is rated at 3500 psi for the following services: Argon, Helium, Krypton, Neon, Nitrogen, Xenon, and Tetrafluoromethane (R14)