Mounting Studs great for spar
From Velocity Aircraft Wiki
These ideas are great for mounting just about anything light and electronic in the airplane, just a couple of different takes.
This came to mind as a comment on another topic but think is better to separate it to a different thread. Here is my approach to surface mounting all around my airplane, including the main spar and firewall. It minimized any holes, anywhere, unless necessary. I finished my third annual in December and everything is as tight as when I installed it. Reiff/Stephen, here is newsletter material you can use when convenient. Jorge's Blog
FWIW, I used these. MacMaster Carr Studs They are about 75 cents a piece. Andy