Well Norm if you were referring the jumper starter shaft on these full crank engines it neither metric or SAE hex. It is a pentagon (5 sided) shape and would require a matching pentagon tool.
As for the valve clearance you probably have either the AC3 or AC4 version. the valve for these engines is 0.003”-.006”(.08-.15 mm) for both valves. The Ryobi AC10 is also the same clearances.
Now my personal luck with these 4 cycles is they are good when they work but are prone to cylinder failures due to the dipper oil system which only oils the engine when upright and not one side or upside down.
