AOA Retro
I had the same problem. Here's what I did:
(from memory--forgive the lack of AN numbers.)
First, I 'plugged' the hole with one standard washer (diameter just fits), then on the inside, I used a large 'bearing' washer. On the outside, I used a Tinnerman counterunk washer.
Then I bolted everything together with a flathead screw and nut.
This plugs the hole and gives a nice finished exterior appearance.
If this is not clear, I could take some photos, but I think if you play with it, you'll see what I mean.
Vern Little
RV-9A (baffles)