I had already drilled the hole in the firewall per the Sonex plans, to run the fuel line through. I decided to penetrate the firewall with an AN bulkhead fitting, which had a much smaller diameter. So I mad a square cover from stainless steel and drilled a hole in it, just big enough to put the AN fitting through.
Then I riveted it onto the firewall, over the hole (photo #2).
The bulkhead fitting was made to secure to a thicker firewall, so I needed to create a "washer" at the interior side of the firewall. I just used a thick piece of aluminum cut to a square (any shape will do), and drilled the same size hole as the firewall cover plate (phot #3).
Now when the fitting was placed through the firewall I put the "washer" over the fitting, and then tightened the AN nut against it. Nice and tight, now!
Stainless steel plate riveted to firewall, after drilliing hole for fuel fitting.
The 45 degree fuel fitting in place (engine-side of firewall)
The bulkhead fitting as seen from the cockpit. Note the aluminum "washer."
