On Wed, 23 Jan 2019 14:50:31 +0000 (GMT+00:00), Jim K.. wrote:

TMH Wrote in message:
On 22/01/2019 14:19, Jim K.. wrote:
charles Wrote in message:
In article ,
Jeff Layman wrote:
I am replacing some old wall lights with some new Där fittings. I was
somewhat surprised to see that the wallplugs and screws supplied were of
different lengths. The wallplugs were 25mm x 5mm, and the screws 35mm x
3.5mm. The diameters match well, but why would you use a 35mm screw with
a 25mm wallplug?

It's because the people who design stuff have never fixed anything to a
wall in their lives & have no idea how to do so.

Rule number 1.

Unpack item, remove screws/plugs, throw in bin.

+1

Rule #2
Use plugs & screws of appropriate size, including being long
enough to reach the supporting substrate behind "render",
"plaster", "whatever". If necessary use more than one plug "in
series".

Just one item had screws and plugs of a decent size, so 0.5% at a guess.
For a professional 'fixer' it must be lower than that.
Had some, for internal use, where the screws were marginal for just brick.
--
Peter.
The gods will stay away
whilst religions hold sway