Lead screw and drive nuts ?

[NB70]

Kammo,

I used the JGRO design for the nut - I attached some pictures below (dimensions are in inches - and you would need to alter the dimensions for a 12X3 central hole). It uses two rectangular pieces of delrin (each around 12mm thick), you can adjust the tension between these two pieces via two bolts to reduce backlash. It would be easier though to just use a single thicker piece and not worry about backlash. These nuts are attached to the machine using four bolts.

Send me a Private Message with your address if you want me to post you the trapezoidal tap. I used a 10.2mm drill for the hole.
DumpsterCNC make all these parts - they are in the USA but post worldwide - http://www.dumpstercnc.com/trapezoidal_12x3x1.html