Just listed a 63mm rear entry pressure gauge, has a scale of 0 - 1 bar or 0 - 15 psi.

Appears to be liquid filled?

I bought it brand new , can't even remember what for, may be of use to some boff, no reserve.


Pressure Gauge 68mm - 1 bar / 15 psi - New In Box - NR | eBay UK

The liquid fill helps damp down fluctuations due to slight pulses in the line (such as after the receiver of a compressor) and vibrations.