PURPOSE: To secure a small auxiliary wheel in a simple forming method, by getting a disc simplified in form and, moreover designing something a contrivance for rubber molding.

CONSTITUTION: To begin with, a rigid plate goes through some processes in which it turns to a disc 3. Next, a stage of work to split the disc 3 to half in thickness to the extent of getting a proper length l from the outer edge over the whole circumference of the disc takes place. In addition, a portion of the halved is set apart into a Y-shape figure in a consecutive process. Finally, a void 5 is left over on the bottom part inside the Y-shape part 4 and then rubber 6 is molded or set in tightly.