Here's the link to the online version of the manual for that engine. It covers most of the smaller Saitos, but it should have what you are looking for.
[link]http://www.horizonhobby.com/ProdInfo/Files/SAITO_Small-Medium_single_cylinder_Manual.pdf[/link]

According to [link=http://www.tru-turn.com]www.tru-turn.com[/link] website your engine should use a 7mm adapter.
[link]http://www.truturn.com/cgi-bin/store/agora.cgi?exact_match=on&p_id=tt0717a&ppinc=adapt0 717a0716a[/link]

Hope this helps

Ken