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The Tecmark Series 3000 switches are "UNIVERSAL". SPNO, 1/8 NPT, 2- terminal. They will work on most hot tubs. The only systems these will not work on is in a air button style system where the heater is powered directly through the Pressure Switch. It's factory preset for 1.5-2.0 PSI which is suitable for most spas. The thread is 1/8" NPT which is the standard used.