Many plastics are difficult to glue to reliably.  Low energy plastics
are the worst.  Not being a plastics engineer, I am not sure if nylon
is such a plastic but this sort of information is pretty easy to find
on the web.

Loctite has a lot of information on the properties of plastics and
suitable adhesives.  Loctite prism 770 primer together with 401 CA
glue will produce an acceptable bond to many plastics of the low energy
and surface insensitive types.  It actually produces reasonable bonds
to acetyl which is a very difficult plastic to glue.  It will even
produce a reasonable bond to surface treated Teflon so it will probably
work with nylon.  There are many types of nylon, by the way, so results
may vary.

The best solution would be to use a different plastic for the nuts.
ABS would look a lot better in black, than white nylon which always
looks dirty and it can be glued to easily.  It can be solvent glued
with "thick bodied" glues that will stick to most porous and many non
porous materials.  Weldon makes such a glue that will stick it to many
metals, wood, fabric etc.

A good plastics engineer could probably recommend a plastic that is
even better than ABS.  If you can find it in hex stock you could just
cut it to length in a mini miter box if you do not have a lathe.  then
drill the pilot holes.  Of course a lathe would make it much easier and
if there are a few people willing to share a manufacturing run, a screw
machine would be the obvious solution.

Spencer Chase
707-984-8356
http://www.SpencersErolls.com