Joined: Aug 2010
Posts: 12,711
Likes: 2,100
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.
The Topline rack mounted light, I had one on a rack and when I went to remove it I found that the nuts were rusted on to the bolts and that the bolts twisted in their plastic mount inside the light.
I suggest you put a nut on each bolt first, then mount it to the rack, and then use a second nut that is stainless on each bolt. Then if several years from now you go to remove it from the rack, you can two wrenches, put a wrench on each nut to unthread it. And maybe some washers too.