Fits many Auto-Pilots.  Flange to flange is  2" 3/4.  Across the face of the flange on the cell.
Mine slides together- No screws- and No radiator clamp.  
DOES NOT fit the  CHLORSync -  Model CS30. Threads are different.
  FYI- This fits the output side of the AquaCal 145  HEATER !!!