Surely it depends on how much of that screw length is outside the wall,
and - if your wall is plaster over brick - how much is in the brick?
I think I'd want a couple of inches in the brick part.
If your wall is breezeblock my experience is that that holds screws
much less well than brick - though maybe that depends on the fitting
*Ramble mode on*
When we moved into this house we discovered, when we took the cupboards down
to fit a new kitchen, that the wall units were held up with two 1.5" screws
at the top of the cupboard, neither of which were tight and one just fell
out with minimal tugging! There must have been some science involved in
keeping the things on the wall - the pressure pushing against the wall
overcoming gravity, or something.
*Ramble mode off*
We used 2.5" screws on the new lot, and more of them.
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