This part is a 5"x 5" Flange Element 5.5kw at 230V or 1.375Kw at 115V with a Gasket, O-Ring and Bolts. This flanged element is found in Plastic Heater housings in Brett Aqualine, Premier  Allstate and Hot Water Products. I have also seen this element in Vita Spa , Streamline  and many others. It features dual 5/16" Thermowells, 1/8" NPT Pressure switch tap, a hole for current collector bolt. Stud for Thermodisc. The flange holes are 4" on center. 

Note: When testing this heater if it trips the breaker simply unplug it and if the breaker stays on plug back in and if it trips this heater is the cause if it is not a breaker trip issue then measure between the two terminals with an Ohm meter it should measure about 10.5K ohms. If it measures 0K it is open. If it is not tripping the breaker and doesn't measure open then the heater is not bad look for other issues that cause no heat Like a Pressure Switch, Stopped up filter, No water movement, Open circuit on board etc…..