It is not in my instructions that came with the engine and I was not successful searching for the info. I want to use a spinner hub nut and need the thread size. I couldn't find it on Central Hobbies site, google , anywhere.

It's an 8x1mm Jack. Here's a link: [link=http://www.geistware.com/rcmodeling/glowpower/ysfaq.htm]Thread Size[/link]

Thanks Tim. I will save that link.