Tecmark Series 4000 switches are 99.9% Universal 25 amp, 2 terminal, SPNO (single pole normally open), 1/8 NPT. They will work on most hot tubs. The only systems these will not work on is in a air button style system. 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.
This pressure switch is used on the Cal Spas 5 & 6 BHP pump owners heaters, known as Cal Spas part# ELE09500204.
pressure switch can be used as a replacement for the 4037P pressure switch.