How about using a Delrin nut instead of the brass(?) one (or a second nut made of delrin to remove backlash)
Cheers. The originals are cast iron, will the delrin be strong enough on their own if I replace them?

Wheres the best place to get ready made ones? as the thread is imperial (1/10 inch) Or is it still cheaper to buy a tap and make them my self?