On Sunday, 25 August 2019 08:48:05 UTC+1, Chris Green wrote:
tabbypurr wrote:
On Saturday, 24 August 2019 10:03:04 UTC+1, Chris Green wrote:
tabbypurr wrote:
On Friday, 23 August 2019 20:33:05 UTC+1, Chris Green wrote:

A well fixed steel screw will hold an incredible weight in shear. My
rule of thumb for steel's strength is 40 tons/sq in which gives a
shear strength of somewhere around a ton for a 5mm screw. The screw
will probably fall out first of course but I do always wonder why
people use great fat fixings for holding a few tens of kilograms.
Nearly all my fixings are 3.5mm or 4mm screws in yellow plugs and I
can assure you they *don't* fall out or break.

Many do. Some suffer from masonry crumbling, or the masonry simply snaps.
Most people fail to clear the dust out, resulting in a weak bond. And the
ida that you can reliably safely support a ton on a bit of 5mm wire sideways
strikes me as decidedly optimistic.

I wasn't suggesting supporting a ton on one screw, I was just pointing
out that big screws are unnecessary. It is of course necessary to
ensure that the screw is soundly fixed in the wall which, I find,
doesn't depend much on the size of the screw. *Longer* screws often
help but *fatter* screws are not a lot of help.

You were. I was pointing out that was not correct. Maybe you're upto speed now.

I said:-
A well fixed steel screw will hold an incredible weight in shear. My
rule of thumb for steel's strength is 40 tons/sq in which gives a
shear strength of somewhere around a ton for a 5mm screw. The screw

That doesn't mean one *should* support so much on a single screw, it
was just pointing out that it's not the screw that is the limiting
factor when fixing things to the wall.

IME it's more often the masonry around the screw or the packing between the 2.


NT