Cheers lads
Spot on Nick ,, it is 5/8 ACME ,,,,,,,,, I use the bench grinder and a screw cutting tool gage ,,, it is easier to start with a length of tool steel first as this makes it easier to hold when grinding .... grinding one side at a time ,, with the tool steel not in the bar .
Then put the tool steel in the bar and lock it up , then you can use the bar as a reference .
Then grinned the other side ,, and cut off the bit you need ,,, i use the good old dremel
Thought i would stick this in ,,,,,,,, just because the HSS comes straight ,,,, it dose not have to stay that way , just heat it up and bend it to suit the job in hand
Had a leisurely hour in the shop tonight and finished off me nut
and made a new bush for the outer end of the screw
Rob