the invention relates to an electric motor having a motor shaft on which motor pinion is or can be placed , to such a motor pinion , and to a method for fastening the motor pinion to the motor shaft . the starting point is a motor pinion having a shaft accommodating section for placement on and fastening to a motor shaft in rotationally rigid fashion , the shaft accommodating section having a wall for encompassing the motor shaft . the advantageous fastening comes about in that at least a part of the wall is fashioned so as to be constrictable for restraining the motor shaft . in mounting , the wall is compressed against the motor shaft by a nut , the wall advantageously having an increasing external circumference .