Thanks both. It rained this afternoon (well all day ) So I made a new one out of brass. I even took some photos for @brightspark !
As I wanted to work out the parameters for cutting the thread, I made an insert for the original nut. Working on the principle that it is under compression when tightened I have soldered it into the original fitting. I'll see how it goes before I make a complete replacement.
Insert thread cut
Original fitting bored to suit.
Now just need to make some new jaws, base skimmed would be good, gib screws need replacing then clean, repaint and see if I can get a bigger milling machine in the garage
@Pete. has shamed me into posting pics of the finished vice! New aluminium and steel jaws made.
As you can see it's a little big for my small mill, but usable, clamps really well, no discernible lift on the moving jaw and a really nice action.