This article is from the Model Rockets FAQ, by Wolfram von Kiparski with numerous contributions by others.
From: billn@PEAK.ORG (Bill Nelson):
Well, you can reinforce the aft ring a bit, then use the screw-in threaded
connectors that are available.
From: email@example.com (The Silent Observer):
Drill a hole on each side, and install a Molly (R) or similar "drive
fastener" or expansion fastener -- the kind used for hollow walls and
doors. Do this with a dowel or motor casing in the motor tube, so the
little metal "legs" on the fastener don't punch through the tube; you'll
find these are about as strong as a blind nut, install from the front,
don't cost much more (if at all), accept standard threads (and come with
a screw!), and look neater. One thing to watch, though; the threads in
the fastener strip pretty readily (they're aluminum) and they're the
devil to remove if you do strip one.
From: firstname.lastname@example.org (Jonathan Sivier):
I retrofitted blind nuts on a couple of my rockets using the anchor bolts
that are available at most hardware stores. These are a metal tube with
threads on the inside and slits along part of their length. You drill a
hole in your bulkhead, push the bolt unit through and tighten the bolt.
As it tightens the tube expands at the slits to push against the back of
the bulkhead. It also has a lip on the front so the anchor is firmly, uh,
anchored. :-) With a little epoxy under the lip it becomes a very strong
mount for motor retention devices. They have different sizes for
different thicknesses of material, from 1/8" up. They may take up a bit
more room than the blind nuts, but if the rocket is already built they are
a great way to make this improvement.
From: email@example.com (Bob Kaplow):
Use threaded brass inserts, and a drop of thin CA to keep them in. They
don't have the large lip on the back, so it won't be as strong, but my
first 3-4 HPR models were done this way. Now I put blind nuts (also called
T nuts) in all my larger rockets. I even use them in motor mounts where I
have the room. DuBro makes some VERY SMALL 6-32 T-nuts that fit most
adapters that have a plywood ring. I've yet to come up with a retainer
for the heavy cardboard tube style adapters.
From: firstname.lastname@example.org (Gary ??, C72500)
If you have already assembled the rocket, look for a "thinsert" and
installer tool. This is basically a threaded rivet -- drill a hole in the
centering ring, put nose of tool (wiith insert threaded on) and squeeze -
permanently installed threaded insert! I have used this to retrofit every
rocket I have built, and have yet to lose an insert or a motor. Installer
and inserts are available through a company called Northern via catalog -
runs about $13.