Heater Element,7.5kw,Dual,2",2 Well Actual thread measurements on 2 inch NPT = 2-5/16 inch Pipe thread fittings (NPT) outer diameter physically measure approximately 1/4 inch larger than the actually size. 240V heaters will operate on 120V just fine but will have 1/4 the performance (6kW on 240V will equal 1.5kW on 120V). Never use a 120V element in a 240V application.