TR8*4 Acme Leadscrews are the standard for the “ZL” versions of the Railcore. Combined with a 0.9 stepper these give you 0.01mm full steps. The difficulty lies in getting good, straight leadscrews as most sources for them are pretty hit and miss on quality.

TR8*2 leadscrews can be substituted, and are available from www.zyltech.com - they also offer delrin anti-backlash nuts. (Note, the yokes use a 16mm spacing, be sure to get the correct leadscrew nuts) These leadscrews have so far been of higher tolerances and straighter than most sources of TR8*4. If using TR8*2 leadscrews with 0.9 steppers you get a 0.005 full step. You'll need to change your steps/mm for your Z axis, and it may possibly limit your Z travel speeds. Use the table below to validate your stepper / leadscrew config, and your settings for steps/mm in config.g

The kits combine a TR8*2 leadscrew with a 1.8 stepper, giving the same step height and steps/mm as the default in the BOM