Looking at this $76 balance master, it says it fits the 75mm and 100 mm bolt pattern. The way I see it, this means it would fit on a rotax 2 stroke gearbox with the 1" boss in the center and it looks like the bolt slots are for an 8 mm (5/16") bolt. The real early 912s had a boss that measures about 1 5/16" and has 100mm bolt pattern, and the later 912s are about 1 3/4" boss with 101.6 mm bolt pattern. Long story short, I think Larry is correct. JImChuk