These are hard to find - we know because we just found 'em! These are a flanged mount high pressure gauge, 0-100 PSI. The mounting flange is 3.5" O.D., and the gauge looks like it belongs in your race car.
It would work for fuel, oil or air, and has a 1/8" male NPT connection on the back. The last time these were in the catalog they were $34.95.
NO WARRANTY, NO RETURNS ON GARAGE SALE ITEMS