Roger Mills wrote:
On 12/12/2011 16:49, wrote:
What *really* matters is whether the fixing can pull out of the wall
and I find that a properly prepared 4mm/Yellow or 5mm/Red fixing is
perfectly capable of being able to hold a suitably sized screw such
that it won't pull out. Most of the weight of a radiator (or
bookcase, or whatever) will just exert a shear force on the screw and
not that much will try and pull it out.
I'm not sure that's right. In my experience, most of the weight is taken
by friction between the bracket and wall - which requires the screw to
be under sufficient tension to hold the bracket tight against the wall.
That's a point I suppose. I don't think it affects my basic premise
though, that a properly inserted 4 or 5 mm screw in a wall plug will
carry a huge amount of weight without problems.
Most of my really heavy weights are on shelving systems that use
vertical supports (steel or aluminium) screwed to the wall so, as long
as the screws are tight, I guess quite a lot of weight is (as you say)
carried by friction between the supports and the wall.
With short pressed steel brackets for individual shelves I guess the
top screws do actually have quite a lot of tension on them.
--
Chris Green