Restoring old lathes, backlash in leadscrews

[irving2008]

OK, a closer inspection and the application of some cleaning cloths showed I was wrong in assuming the SuperRelm was like its smaller brother. Where the RelMac has the leadscrews working directly into the cast iron, the SuerRelm is more sophisticated and I found, after moving the tool carrier and cleaning 85 years of gunk off, a screw head. Further inspection revealed a bronze/brass nut held in by a screw - see pics.. this is the topslide, but the cross-slide also has a screw head only visible once the topslide is removed.

It is 8tpi LH x 3/8", I measured it accurately with the digital calipers. RDG do a 3/8 x 10tpi LH tap for £10 but not an 8tpi :sad:, then again i dont want to be making a new screw if I can help it...

I can move the nut back and forth about 1.0mm on the screw. And the screw's endfloat in the brass bearing/mount is about 0.3mm but thats easily rectified with a washer under the handle

How do I measure wear on the screw - is it likely to wear or can I assume the wear is all in the nut?