Originally Posted by Bavafa
Nice mod and thanks for explaining. Are you planning on putting a safety wire on the plug?
This looks like it was machined to accommodate for the o-ring.
I do safety wire the plug through the filter housing to the filter base, same piece of wire...easy.
I do it out of habit, although I've never actually had an oil filter come loose on anything I've installed one on, including an enduro bike which gets much more vibration and pounding than any airplane ever will...but that's a topic for the "to safety wire, or not to safety wire your oil filter" debate list and probably not what you're asking.
The plug opening is in fact machined for an o-ring. It was milled to the dimensional standard for an AN814-4 plug, but not anything I take credit for - I bought it from K&P Engineering that way. (usaoilfilters.com)