Gmf lathe

[MEGGSIE2]

Hi
I have a GMF K-1440 lathe and was wondering if anyone could tell me what size and thread the headstock spindle is as i would like to buy a chuckjaw but do not know what size insert i need.

[Treecycle]

But it doesn't appear they got a manual that time. Most of the manuals for this type of lathe don't list the thread size anyway.
Best option is to get someone who knows a bit about engineering to measure it and they could work it out from there. It is likely to be the same as the other generic lathes that look like that including the GMC which I believe has a 3/4" x 16TPI thread, which is 3/4" UNF. If you can get hold of a nut of that thread and try it on the spindle it will tell you if that is correct or not.