In article ,
says...


asalcedo wrote:

I need to screw 100 to 120mm, gauge 12 (5.5 mm diam) screws onto plywood
on top of hardwood (joists)

Why such long screws? I'd use 50mm or so (and probably an 8 or 10
gauge) for this.

All the load is being held by the joists. The screws are mainly
stopping the ply floating around. Slightly different if you're building
a box section, but even then I can't see that longer screws add much.

I was a bit surprised by hardwood joists too.