Quick description of diferences between St. John and CDF rotors: St. John rotor always at full diameter. Rotor bars on St. John rotor are mounted flat, as opposed to tipped forward as on CDF. This enables use of 3_4" space bars in all crops, and rotor feeds more aggressively -- won't slug in soybeans and wet corn as CDF occasionally will. less cylinder RPM required -- less likelihood of grain damage, and trash isn't torn up as badly. Discharge paddles eliminated on St. John rotor. No reverse bars have ever been required on a St. John rotor. Hope this helps.