delete

[ramblinChet]

delete

 

[billiebob]

Either an elevator bolt or a carriage bolt and thru bolt it. Or a tee nut and bolt, and thru bolt it.



With a tee nut and bolt you might need to cut the bolt to the correct length.

 

[simple]

Looks like you have put a lot of thought into this already. If the plywood is solid, I would think 6 stainless steel 1/2" #10 pan heads should do the job. I might put some sealant / adhesive on the threads like 3m 5200.

 

[NatersXJ6]

I wouldn’t trust any screws that short not to rattle / back out of plywood. You can put some sort of glue on them to reduce the chances, but without through-bolting I’m guessing you don’t get 2 years before loosening is an issue. That being said, if you insist, I would use something like a #10x3/4 stainless Sheet metal screw, hex head for driving force, with a lock washer under it and drill the smallest possible pilot hole (1/16”) and apply something like bar soap to the threads. Use a sharpie to draw a reference line across the head so you can see if it is backing out over time.