Originally Posted by Rowan
]meaning there is metal against metal, rather than creating a plastic sandwich.
I have a Jannd lowrider on front, on a one-eyelet Schwinn. Aside from the plastic sandwich (a good point, though I have Gilles Berthoud steel fenders and aluminum mounts) putting the frame next to the fork puts less bending moment ...i.e., stress, on the bolts/studs/screws that go into the eyelet, therefore less chance of breaking a bolt. This could be a catastrophe, if something drops into the spokes.
Rather than using those little silver allen head screw/bolts that come with the racks & fenders, I strongly recommend 5mm allen head machine bolts, which can be bought in all lengths at auto parts, Lowes, etc., and secured with blue Loc-Tite.