Fits 6-32 and 4mm nuts, fits all hollow rails with a reasonable wall thickness, all three versions, that fancy (not super fancy) spring holds it in place while you fumble for some screws.
I like it a lot. As a thought. What if you moved the flap so it was closer to the nuts. Maybe it would help hold them in place as well. I didn’t use glue like you suggested and the nuts kept falling out.
I considered printing 2 extra just to use the extras to hold the nuts in place before the bolts could get threaded.
I really wanted to make a holding spring but you can’t really do it. Too close and it will fuse, too far and it won’t do anything. A piece of tape isn’t too bad on something you will only see once. I stared at it for 2 days trying to do just that…but tape is okay with me at this point. I used my CAD momentum for a bigger project…details after testing.