Originally Posted by
HillRider
One alternative to drilling and tapping the hole for a larger bolt is to thread (or push through if the threads are really stripped) an M5x.8 bolt from the inside of the dropout toward the outside. Use a bolt with a button head or pan head so it has very little thickness on the inside of the dropout. File the head a bit thinner if needed. Then install your rack, fenders or whatever and use a nut on the outside of the bolt to fasten it in place.
That way the thickness inside the dropout is minimal and shouldn't interfer with the chain or small cog the way a nut on the inside would.
I have done this with my Trek 7500FX which has an aluminum frame and I was mounting a rack for loaded touring. I ground the head of a stainless pan head screw (Phillips drive) to about 0.5 mm thick and screwed into place from the inside on the cassette side. The little tiny bit of the Phillips drive that was left helped to hold it still while I screwed the nut on tight.
I did this before the threads were stripped, thinking that the 40 lbs on the rack was going to wreck the threads if I didn't take some preventative measures.
Well, it held fine and 3 years later it's still there.