That's what I was thinking.. except for what looks like a valve stem in the OP's picture.Looks like an air hose quick connect coupler, like these...https://www.amazon.com/Industrial-Connect-Adapter-Compressor-Fittings/dp/B081F9K54B/ref=pd_lpo_2?pd_rd_i=B081F9K54B&psc=1
I've got a Schrader valve on my TPI.What would be a standard test port for a fuel pressure gauge?