Electric heating units and electric heaters, namely, strip heaters, over the side heaters, flange heaters, ring heaters, flexible heaters, band heaters, nozzle heaters, cartridge heaters, screwplug heaters, tubular heaters, radiant heaters, industrial air heaters, boilers and steam generators, circulation heaters, fluid superheaters principally for industrial purposes, fluid pre-heaters principally for industrial purposes, tank heaters, liquid heaters, immersion heaters, and electric heating ...