I am using my own hardware while building the Scura and the nuts I have don't fit snuggly in the holes for them. I found this frustrating, when test fitting the M4 screw to hold the top on. Yes, I could have used glue or filament from a 3d pen as a solution to hold the nut in place, but then I remembered that I had purchased some m3 heat set inserts and some m4 rivet nuts. They are set by using a soldering iron to heat the metal and soften the plastic.
I replaced the m3 nuts in the top body with these. They were long enough that I can now use m3x40 screws instead of the m3x45 in the plans.
The m4 rivet nut was also used in the top body piece, but it isn't as secure and it caused some problems because plastic blocked the opening. It works and doesn't seem to fall out, but I will need to be careful of overtightening since it may cause the piece to spin. A m4x16 screw works with this even with the viewfinder attached.
Things I would change: use a screw to align the insert with the part. this will also keep the hole open rather than filling with melted plastic. I have ordered m4 inserts, because the m3 inserts worked so well. I might replace some of the m2 nuts too.
I am happy with the results since I don't have to chase nuts when putting it together (I still have the tiny m2 nuts) and don't have to worry that I will need to take the whole thing apart to get that m4 nut back into place.
I am really enjoying this project. It is bringing together so many things that I love.
These are the inserts I am using. They are meant to be used with 3d printing. These allow for greater torque and pull strength. There are other inserts that are designed for injection molding, and are extremely common on Amazon, but aren't as strong in printed parts. There is a video by CNC Kitchen where he tests different connections in printed parts. Captured nuts are among the strongest, but may not always be ideal.