On Fri, 17 May 2019 21:42:59 +0100, dpb wrote:

On 5/17/2019 3:23 PM, Commander Kinsey wrote:
...

I can imagine the actual screw taking a fair sideways load, but it'll
gradually work it's way loose in the wood.

What do you mean by "sideways"? The screw is in tension, not shear.

It's in shear. The force is downwards, the screw is horizontal.

As far as loosening, in an application like this, it'll still be there
when you (and your grand-kids) are long gone.

Put a woodscrew into some wood. Wiggle it. See what happens.