Maybe the rod needs a little play and fixing the nut holder with screws allows one to loosen them? However the T8 is fixed with screws in the T8 nut holder. So if you want some play in the T8 nut, you could just loosen those screws. Is there maybe some other reason?

You probably right if it s better think to printed the holder and screw togather and get some settings with the orignal screw holder. If i understand correcly

I am not sure I understand what you said...probably lost in translation ;)