Response to Hello Roberto.  The attachment threads of the Pentair Filter Pressure Gauge w/ Indicator Rear Mount, OEM - 190059 are 1/4" NPT (National Pipe Tapered Threads).  NPT threads taper at a rate of 3/4" per foot.  Per NTP Technical Specification the outside diameter of the 1/4" Nominal Pipe Size is 0.540".   Most pressure gauges (top mount or bottom mount)  in the pool & spa industry have identical thread patterns, 1/4" NPT with an outside diameter of approx. 1/2".

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