Bicycle operating device, bicycle adapter, and bicycle assembly

A bicycle attachment structure for coupling a bicycle operating device to a handlebar clamp coupled to a handlebar, the bicycle attachment structure comprising:

• the handlebar clamp including a first hole;
• a base member of the bicycle operating device, the base member including a second hole;
• and
• a bicycle adapter configured to be disposed between the handlebar clamp and the base member,
• the bicycle adapter including a first attachment surface, a second attachment surface, and a nut insertion hole extending through the first attachment surface and the second attachment surface,
• the handlebar clamp, the base member, and the bicycle adapter being configured to be fitted together such that the first hole, the second hole, and the nut insertion hole are aligned with one another with the first attachment surface facing an outer surface of the handlebar clamp and the second attachment surface facing the base member,
• each of the first hole, the second hole, and the nut insertion hole being configured to allow a fastener to pass through,
• the first attachment surface having a first curved section, and
• the second attachment surface having a second curved section that is different from the first curved section,
• the second curved section being less curved than the first curved section.