In reply to Garbhanach:
Hi, I knew it wasn't a standard tripod mount as it is definitely under 1/4". It is closer to m5 than m6 but I can't find a thread guage or any reference to this size of mount online.
If I can mount it off this it would be improve the balance a bit as the camera is a bit nose heavy with the adaptor, x2 and a fairly heavy old telephoto on it.