I need some guidance on how to securely install a ceiling fan on my aluminum structure patio cover with an acrylic roof. I have a double-walled beam (attached image for reference) where I would like to mount the fan. However, there is a C-shaped fold on the edge of the beam, which makes it challenging to use bolts and nuts for installation. 
My initial idea was to attach a fan box to the beam using self-tapping screws. However, I am concerned about the fan's torque potentially causing the screws to loosen over time, leading to the fan falling. I would greatly appreciate any advice or suggestions on how to properly and securely mount the ceiling fan to the beam in this specific situation. Are there any alternative methods or specialized hardware I should consider to ensure the fan remains stable? 
Not saying it will be fun, but it looks like just enough space there for a nut and wrench without too much pain. I have had a lot worst places to work in that caused some unladylike language.
Commented May 18, 2023 at 21:21Any reason you can't attach a new I-beam to the webs of adjacent roof beams (like an H) and bolt your fan to that?
Commented May 19, 2023 at 13:23@crip659 what size bolt and nuts should I use? I chatted with someone around me and he thought in using 3/8" bolts. I don't think these would fit in the space.
Commented May 19, 2023 at 16:34@Huesmann I talked to someone around my area that had the same idea. I'm pricing out the materials to do that. It will definitely be more expensive than just attaching a bolt to the existing beam.
Commented May 19, 2023 at 16:345/16 grade five, should be plenty. A flat washer to spread out the force plus a lock washer/nut(or locktite) so it does not come loose. The ceiling fan instructions should have sizes required.
