[smhertzog]

The C motors have a threaded on bell end with a set screw to lock it in place. The smooth cans have indentations (crimps) in the can to lock it onto the ends. The heat sink being part of the c's case draws heat away from the motor better than a smooth with a heatsink. If you do get a smooth can use heat transfer paste (artic silver) between the sink and the motor case.