The coupler is released from the pump shaft by loosening the set screw with an Allen wrench. The set screw rests in a blind hole along the shaft; the set screw must therefore be backed off at least 1.8" before attempting to remove the coupler. If stuck, a screwdriver may be used to gently pry the coupler from the shaft (before prying, be certain that the set screw has cleared the depth of the blind hole – usually about three full turns of the wrench will clear the hole).