Heaters with 1 inch plugs. Standard built-in thermostat is a one pole device limited to 240 V 25 A. Whenever the heater voltage exceeds 240 V or the heater current exceeds 25 amps or for three phase supply, the thermostat is intended for pilot duty only and is not factory wired to the elements. Type CXF are used primarily for oil heating and have steel screw plugs. Low watt density heaters are used in heavier, non-circulated oils. Higher watt density heaters are suitable for light oils or in forced oil circulation loops. Incoloy® elements are silver brazed into a steel screw plug.