Hope this is the right forum for this. I would like to know how strong the couplings that attach the motors to the screws should be. Motors are 425 oz nema 23's screws are 10tpi 1/2" acme's machined to 1/4" at one end. I made some with 1/4" id 3/8" od hdpe plastic tubing with 1/2 x 1" x 3/8 id high density plastic bushings tapped for set screws to attach at the ends (too weak) then I sleeved them inside with a very thin aluminum tubing and hdpe (again a little weak). I don't want to make them too strong as I would rather replace these than the alternatives. What if I were to use steel thumb shrews (drilled out and tapped for set screws) Would these be okay? Also, I've considered drilling out a piece of 3/8 or 1/2 aluminum rod (set screws again)? any help will be greatly appreciated.