This is a new TEMCO 1/2" NPTF Brass Fuel Gas Tank ROLLOVER SAFETY VENT VALVE Assembly.

Brass Roll-Over / Tip Over Gas Diesel Fuel Tank Safety Vent Check Valve.  The fitting threads into the of fuel or gas tank to allow air to enter or escape as needed.  It also has a check ball inside of it so if your vehicle tips over and is upside down fuel will stay in the tank.  1/2" NPTF Pipe Thread male mounting threads and accepts a 5/16" ID hose.

Hose Fitting OD:                           5/16" or .312"
Thread Male Mounting Threads:  1/2" NPTF
Valve Action:                                 Tip/Roll Over Ball Valve
Material:                                        Brass
Length:                                          2 3/16"
Vent Flow:                                     30cfm or .23psi Max Back Pressure
Hex Head Size:                             7/8" socket or wrench to install
Temco Part Numbers:                   90-00945 or 9000945
CFH:                                             Up to 70 Cubic Feet Per Hour