Plywood in this orientation probably isn’t the best material, but I think it would hold up pretty well. Sticking a washer under both the screw head and the nut would spread the load and help out. I used a #8-32 screw in there because it was what I had on hand. If I remember right a #8-32 is good for over 500lbs of clamping force; so it’s more than adequate for most situations it think. I think one way to increase the strength would be to:
- Use hardwood
- Better plywood
- Drill an over sized hole that would allow you to glue a dowel in place and then drill the hole for the screw through the dowel
I did this just as a proof of concept… it definitely needs more testing. 