Thank you for your response.
My infill is OK, and I had no issues, I added 4 perimeters to ensure strength for such narrow vertical print. FYI strength is mainly in perimeters not infill, you can test yourself ;)
All recommendation are generic, as you thankfully shared step files, I easily customized it according to my needs including tightening threads.
General recommendation on creating threads: Set same setting for both internal and external threads (male and female). Then Push one titled side 0.1 to 0.2 maximum to allow easier assembly. If on purpose you would like to make the parts more lose for any reason, push the parallel side 0.1mm, that would make it really loose.