William,

If it is all like you and Christopher are saying, than nearly all applicable four-strokes are AAC, ABC and ABN.

But being ringed (are there any ring-less four-strokes?), they don't have a conically tapered sleeve.

I stand corrected then.

What about the OS.50SX and OS.91FX; do they also use brass base metal sleeves, or are their sleeves made of steel?

Is everyone going back to Super Tigre's ABC ring arrangement?