Another Marvel of Chinese manufacturing

[Clive S]

The bearings indeed have a writing on them it is 5001Z. I got BK and FK Blocks and neither are working. I got them from a local seller.

Those are not BK blocks, BK are like this :- https://www.google.com/search?safe=a...V6WUHewkEU1-M:

AC bearings a bit like these:- https://simplybearings.co.uk/shop/p8...duct_info.html

5001Z bearings are not good for ball screws you might be able to get the AC type and fit them back to back.

Your blocks are FK and FF:- https://www.google.com/search?safe=a...8ASwh55BuW4nM:

Looking at your housing is there a spacer tube in the bearing seal? Look at the picture of the BK block above you can see a spacer at each side