there are 2 layers of 1/8th" ply that are glued together.

12 1/2 " outside dia.

the ring is 3/ 16" all the way around.

there are 4 tabs spaced evenly all the way around that have drill mark that are 10 7/8th " apart.

or 7/8" inward from the OD

the tabs extend 3/8th" inward from the dril holes

shoot me a PM if you have more questions.

Hope it doesn't make my sound in a super way...

I flew my GP GB with a OS 120 FS , fun, fun, fun