The Delrin Acme Lead nut is used for Z axis actuation on the Shapeoko, XCarve and many other robotic and CNC applications.
The Acme thread is shown for example, this item and price is black nut only.
Its secured to the machine with two M5 * .8 Bolts (threads in the nut)
The ACME nut TPI = 12 / pitch = 2.117
In the Shapeoko/CNC application, using 2 Microsteps, steps per mm is 188.946623 Steps Per Revolutions * Microsteps / Pitch
200 * 2 / 2.117 = 188.946623
NOTE!!! If you already have a screw, be careful that it is also the imperial ACME thread and not the metric Trapezoidal screw - they look similar but... are not!