Backlash adjusting nut for linear stepping motor.

I designed the backlash adjustor for linear stepping motor.
The backlash of linear thread nut can causes problems on the position accuracy when reciprocating movement.
The two of thread nut can prevent the backlash on the linear thread.
Two nuts are assembled with LM8UU holder as following link.
http://www.thingiverse.com/thing:86191