Guys I live in NH and they are required for oil and gas burners. They are thermo cut-out switchs. The type I see around here are black with a push in black "switch" which has a temp rating of I believe of 185 degrees which is supposed to melt at that temp and shut off the heating equipment(It is wired in series with the hot wire). This is also known as a "new england safety kit" which includes the fire-o-matic, a switch at the head of the basement stairs with red plate(oil or gas) and a fire-o-matic on the oil feed that looks like a black wheel and is used to shut off the flow of oil to the burner. This also has a temp rating and will melt if there is a fire and shut off the flow of oil to the burner.
