The diameter-length ratio, slot-tooth ratio and the pole number can principally be chosen freely when designing a special induction motor for inverter supply. This paper deals with general aspects on these design parameters. Special attention is paid to motors requiring a high pull-out torque, such as traction motors. It is found that a traction motor should normally be an "iron motor". Moreover, it is found that the potential to increase the pull-out torque when making a slim motor is due to secondary effects like reduced end-turns. Finally, it is found that a design with four poles is seldom far from the optimal pole number. For high-speed drives two-pole motors are sometimes better and for traction drives six-pole motors are sometimes preferable.