Abstract: A plurality of square projections 26 are arranged in two mutually perpendicular directions at the pitch of P on to the surface of a plate member 27 between a first group of punched recesses 29a. The pitch P is twice the length of a side of each punched recess 29a. Shifted with respect to the first group of punched recesses 29a by P/2 in both the vertical and horizontal directions is a second group of punched recesses 29b. The punched recesses 29a and 29b define the projections 26 in the parts which are not occupied by these recesses generally in the pattern of a checker board. Because the projections 26 are separated from each other, and can effectively dissipate heat therefrom, the increase in the contact resistance due to heat generation can be prevented, and the efficiency of the starter motor can be increased.

Abstract: The capability of heat dissipation from the contact surface of a magnetic switch for a starter motor is improved without increasing the fabrication cost. A punch 28 having a plurality of square projections arranged in two mutually perpendicular directions at the pitch of P is applied to the surface of a plate member 27 to form a first group of punched recesses 29a. The pitch P is twice the length of a side of each punched recess 29a. Then, the punch 28 is shifted with respect to the first group of punched recesses 29 by P/2 in both the vertical and horizontal directions before forming a second group of punched recesses 29b. The punched recesses 29a and 29b define projections 26 in the parts which are not occupied by these recesses generally in the pattern of a checker board.