What is the difference between this and a 1-pole or 2-pole contactor

How do I test the defrost cycle on this board

Engineered for high-flow efficiency

which provides the structural integrity required for mounting building automation hardware while offering superior protection against oxidation

Spence Engineering TA120220 Thermo Assembly 30067439-890 What is the difference betweenThe Spence Engineering TA120220 Thermo Assembly is a heavy duty vapor tension thermal element designed for precision temperature control in steam operated systems. Built for compatibility with the Spence T14 temperature pilot and Type E main valves, this assembly operates within a specific 120 220F temperature range, making it a standard for storage heaters, jacketed kettles, and large scale domestic water heating. This replacement Spence thermostat