Square Ballnut??

[Jonathan]

have you got a link then??

Have you got google then?

its not that expensive for the ballnut [...] the alternative is machining out under the bed where the nut will be mounted.

About £60 with vat, so almost 3 times the price of one RM1605 in China. I know which I'd rather... for the price of that ballnut you could get two Chinese ball-nuts, Belleville washers and preload them to get zero backlash with money to spare to make the mount. To me it would be well worth machining the bed, may not even need to if you used RM1204 ball-nuts as they're significantly smaller than RM1605. Since you wouldn't have to machine the ballscrews the overall man-hours is probably quite similar.
What machine is this for?