I ordered a bunch of random sizes from aircraft spruce just for the avionics .. I don't recall which ones I used but they fit well. Try #8 .. not many options, you can't really adjust that hole.
Edit: Also test fit the unit once you go down a size, even if it's slightly proud the unit may not touch the screws, I remember this being the case with mine.
#140376 RV-14A QB IO-390 Thunderbolt
Progress: All Kits Done
Last edited by bkervaski : 01-03-2018 at 01:10 PM.