Good luck on that one.
I just pulled mine out to measure it for you and got a strange suprise.
It actually checks to be M 11x.75 however according to my machinery handbook (24th edition) there is no such thread as a standard.

Coming from China at that time it doesn't shock me. I made a pretty good living for a while americanizing machine tools that came from over there when US companies attempted to save a ton of money. I saw some crazy ways of doing simple things. It didn't take too long and they started using standard methods.