The rear bolts I know are shouldered/stepped bolts that have a rubber grommet over them. Not sure how good your fenders are but on most I've seem to date the holes in the femders are worn, I ended up buying some 1/8" rubber sheet and cutting some washer sized pieces to sandwich between stainless washers. It's worked well and doesn't look out of place.
I'm sure that all the fender bolts are 6mm (all are metric that I've seen) those front two I'm assuming are the ones just infront of the tank? They are about 20mm long by M6 thread (6mm)
I'm sure that all the fender bolts are 6mm (all are metric that I've seen) those front two I'm assuming are the ones just infront of the tank? They are about 20mm long by M6 thread (6mm)