The powerheads I have worked with have a twist off compartment that holds one end of the rotor. You have to be able to get to the rotor, because you need to clean it and the inside of the driving coils or it eventually locks up. The removable part is the part with the inlet (center) and outlet (outer) passages. I had to use a pair of pliers, gently, to turn the one on the Catalina powerhead so it would come off.