Joined: Aug 2010
Posts: 12,748
Likes: 2,108
From: Madison, WI
Bikes: 1961 Ideor, 1966 Perfekt 3 Speed AB Hub, 1994 Bridgestone MB-6, 2006 Airnimal Joey, 2009 Thorn Sherpa, 2013 Thorn Nomad MkII, 2015 VO Pass Hunter, 2017 Lynskey Backroad, 2017 Raleigh Gran Prix, 1980s Bianchi Mixte on a trainer. Others are now gone.
If you use the same bolts for both the rack and fender:
Rear - you want the rack to be next to the frame dropout, the fender outside of that. If you had the rack outside of the fender, that is weaker when your rack is not touching the frame mount.
Front - you can put the rack on the outside of the dropout and fender mounts inside of the dropout, in which case you need long bolts and nuts to attach the fenders. (I do not use disc brakes, not sure if this would work on such bikes.)
I also use blue locktite on all rack bolts.
Avoid the button type heads that use a 3mm allen wrench, the heads are not as strong as the bolts that use the larger heads. They work fine for a water bottle bracket but otherwise are too weak for a rack.
I carry a few extra bolts on my frame at all times. On my LHT, I use all brazeons, but for the rear rack mounts on the seat stays, I have a few extra bolts, washers and nuts threaded into the other side of the rack mounts.