Engine rim and base
B3 rim = shield without mounting options. Used together with the base for direct drives (pulley, clutch, sprocket, etc...)
Large flange B5= screw-on flange larger than the diameter of the motor housing. It is used when connecting to a gearbox.
B14 flange = screw-on flange roughly equal to the diameter of the engine housing. It is used when connecting to a gearbox.