I have approached 2 UK companies that either supply or manufacture and supply ball screw units.

One looks very encouraging as having checked, it looks like i can get away with a 12mm screw diameter based on their technical drawings.

It appears that the OpenBuild machines all use 8mm ACME thread and the nuts are... a bit of a surprise?

Would love to see the comments from Jazz when he see's these!! What a pile of ........................
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Anyway - will let you know once i get some replies?

Or the other option is, i get something like the attached images made up to run on my 16mm screws?

WoodKnot