Tecmarks pressure switch is easily the most common in the marketplace - Tecmark have been supplying this same style of adjustable pressure switch for the last 10 years, this switch is stainless steel.
If the wheel mechanism has become stiff resulting in re-setting the switch, the unit needs replacing. Failure of a flow switch usually produces a FLO error message or three flashing lights on the topside control.
Connections: 1/8" MPT screw thread (connection to heater) / 2 x flat spades (connection to contact wire)
A huge variety of spas and systems, too many to list
The pressure switch is sometimes encased in a plastic housing, don't worry, it is the same switch & is extremely easy to replace.