I didn't originate the idea, someone else here thought of it first. I saw it in a post a while back.

It's an easy mod. Just file/grind off all the parts on the back portion of a Dia Compe brake arch that stick up until it is flat, then smooth it off with progressively finer sandpaper until you have hidden all of your file marks.

Then for funsies I put in an M7/M5 thread reducer after tapping out the center hole to M7. I fixed it in there with a dab of red locktite so it would stay. Now I can hang the fender and the mini-rack from that without worry about messing up the aluminum threads it if gets removed/replaced a few times and I can use a common M5 bolt.