hi, I am wondering if you could ask someone else to screw them together. The reason I say this is because I have an issue with my muscle strength at times and it is actually quite common. There is a possibility that if you have a bit of arthritis (in hands or neck), carpel tunnel or any bit of inflammation it can lead to muscle weakness. I first noticed mine when I was using scissors. I kept sending the scissors out for sharpening thinking that they were dull when all along my fingers were too weak to cut sutures. If I was quite busy with my hands I noticed I had trouble picking things up. If I rested my hands for a moment or two then I could resume the task. I can't trust myself to adequately tighten anything unless I rested my hands for a few moments to renew the strength in them.
Just a thought as others have said that they don't have problems with their set.