If you add an attachment bolt where there's no mounting hole then, yes, a hole must be added/drilled. (Care taken due to the thin fender material, sandwich/support the fender with layers of something).


The reason to have this added point of support is to minimize the fenders flexing vertically, which in time will cause the fender to work harden then crack near the crown mounting point. Usually this is worse on the rear fender that has a greater length past the bridge mount.


The leather or plastic washer is to reduce the vibration locally at that attachment point. fenders have very little "wall" thickness and tears/cracks at the mounting points are not uncommon. So method to reduce flexing and vibration are more then just keeping the ride over bumps quiet. They also extend the life of the fender. tThere's a common hardware item called a "fender washer" which is a washer with a large OD compared to the through hole. Better to support a sheet metal fender with a larger support area. Andy