I've solved that problem of "miscalibration" of the printer, but in the end I found it was just the fillament's color problem.
Originally I tried to print in red and then I tried black and white and they fit perfectly on the tubes.
Anyway I'm writing to you to ask in the part's table the "Nut Lock" how many copies should I make? In the QTY you've got only 1 piece but in the total time you've got the double of the "Time/part".
So what is it really, one or two pieces?
Thank you once again!