Yep, it is 10mm. But there are at least two different threads. Moki uses a 10x1mm. As opposed to 10x1.25mm (used on some Super Tiger, Zenoah and MVVS engines).

Moses

edit: Not sure Dave Brown makes an adaper for the Big Moki's. Try a Tru-Turn or in the alternative Harry Higley makes a 10x1mm spinner nut.