Gap adjustment member, method to assemble gap adjustment member, and transmission

A gap adjustment member interposed between a first member having a mounting hole, an annular groove concentric with the mounting hole, having a diameter larger than a diameter of the mounting hole at a bottom portion of the mounting hole, and at least one recessed groove recessed toward a radially outward direction of the mounting hole and extending from an opening of the mounting hole to the annular groove, and a second member mounted to the mounting hole, the gap adjustment member inserted in the mounting hole and disposed in the annular groove, so as to adjust a gap between the first member and the second member, the gap adjustment member comprising:

• a main body portion having a diameter less than or equal to the diameter of the mounting hole;
• and
• at least one outward protrusion protruding radially outwardly on an outer perimeter surface of the main body portion, a number of the at least one outward protrusion being less than or equal to a number of the at least one recessed groove, and
• a diameter of a virtual circumscribing circle, which circumscribes the main body portion and passes a projecting end of the outward protrusion, and a crossing point, in which a virtual line that passes the projecting end and a center of the main body portion intersects the outer perimeter surface of the main body portion, and which is the crossing point on the opposite side of the projecting end, is greater than the diameter of the mounting hole and less than or equal to the diameter of the annular groove.