I have 4 Anti lash nut blocks. Two seem to work fine. Threading is smooth and easy and they are working great. Two others are very problematic. It is very difficult to get the same lead screw that the others work fine with to start on these two. I can force it to thread of the small side but it won't go all the way through - it won't thread at all on the wide side. This is with or without the small screw installed.
Openbuilds Canada sort of - (Makerparts.ca). They were great and sent me a new one but same thing. Two earlier ones work perfect. also - this is a comment note from another user in Jan 2019 on the parts store - "Overall quality is great! Solid machined block , not injection molded. Accepts almost any type of lube, quiet operation. Downside, there super tight! One block of the pair I ordered is tighter than the other. They’re so tight my 2 amp nema 17 motors cant turn the lead screw. I have tried a handful of different lubes and ran them back and fourth with a high speed drill. They’ve broke a bit but are still very tight. I drill them out today by 0.080” and they seem to be significantly better. Next step is try them again, fingers crossed it’s enough." Did the manufacturing / fab change or is there just a bad batch out there?
Tolerances do come into play sometimes. Tight is expected (better than loose with lots of play) and can be bedded in with a little leadscrew action chucked up in a drill. Of course on the reviews you can't say for sure if both screw and nuts came from us - our leadscrews are custom rolled to be a bit undersized to better handle that But that is not typical of our Leadnuts - though we have seen knockoffs where the thick part was not threaded at all, that's what lead to my question about who its from Speak to MakerParts, ask them to replace them, and let them test them on a leadscrew before shipping them out