I just use tee-nuts in the 6-32 size and buy hex head 6-32 screw that I can drive with a ball joint hex key.
The trick is making the clips. Check QQUAKE's build threads as he almost always posts pictures of his retention system with details. I use brass strip, he uses aluminum(?) I think. The retainers are nothing more than a means to keep the motor case from kicking out during the deploy charge going off. I drill a hole in the end, bend the strip in a vise to form the Z shape and file off the rough edges. The trick is to measure the lengths and mark the bend locations with a Sharpie. Tighten the strip into a vise so the marks are just showing and then tap with a hammer to bend the strip. You can get fancy and make sharp bends or you can leave them rounded. I usually make square bends at the bottom and round bends to hold the motor closure lip. YMMV. Like most things, you'll get better at this after you've made a few.
Not shown in the attached picture is that the tee nuts should be secured in place with epoxy, preferably JB Weld. At least that's what I do and I learned that from Jeff the Handeman's builds threads. If you use the toothed tee-nuts and press them in with a vise, I'd still recommend the epoxy. Maybe it's a belt and suspenders thing but if it prevents disaster, it's worth the effort.
Kit (AKA Cranky Kong)
Total Total Impulse as BAR: 7,753.69 Ns (Equivalent to a 51% M motor.)
=| Calirado, Colofornia...what's the diff anymore? |=