Suntour offered an 11 tooth cog. Since chain clearance is an issue, the cog was undercut and you needed to use a special lockring.
OT: While googling Suntour Cog I was presented with this.
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This is Africa, 1943. War spits out its violence overhead and the sandy graveyard swallows it up. Her name is King Nine, B-25, medium bomber, Twelfth Air Force. On a hot, still morning she took off from Tunisia to bomb the southern tip of Italy. An errant piece of flak tore a hole in a wing tank and, like a wounded bird, this is where she landed, not to return on this day, or any other day.