The M-4759-6 is a 0-600 PSI liquid filled pressure gauge that has a front O.D. of 3 5/16", glass face diameter of 2 1/4", back steel case fits a hole size of 2 1/2" O.D.. This gauge is a flange mount with 3 - 1/8" holes on the flange for mounting and an 1/4" NPT threaded connection on the back. (Image shown is a 0-200 PSI Liquid Filled Pressure Gauge.)