This is yet another revision of this design but it has been modified so that you can choose between 3/18-12 or 1/4-16 ACME leadcrew lead nuts. The printed lead nuts actually work really well. I've tried them in both PLA and PET and really can't complain. They eliminated my backlash issues due to a much better fit than the standard supplied metal nuts, which had a fair bit of slop. Not to mention the thread just glides though them. Like the previous revisions, It's designed to take advantage of the aluminium blocks on this carriage to bolt into, making a much firmer attachment. Stock, PB recommend you bolt the leadscrew supports into plywood holes on the carriage, which strip easily and flex a lot, causing banding.