Matt
This is a Sieg lathe made in China, the tool post stud is definitely not imperial. I have a similar machine and when I put a QCTP on mine it came with a suitable sized stud to replace the original, and works fine. I would check the thread in the topslide for damage and if necessary run a tap through. Of course if you bought the lathe secondhand a previous owner might have done something weird.
Regards
Martin
Edited By Martin Shaw 1 on 02/02/2018 21:44:22