Hi Jake,
I'm not sure I would can it a "Tono" that is more of a traditional Mongolian yurt term ...
There are 5 separate pieces (purlins) that set into mortis joints which comprise the perimeter of the central skylight openings.
It is a pentagon so it doesn't have a diameter, but the span across the center averages out to 78 inches.
This is a ten foot 'travel' yurt being built inside a 20 foot 'tri-wall' yurt.
-G'day