I would start to worry around 20 kg. Probably worth having 2 screws then. I fitted one the other day must have been 25-30 kgs, it was supplied with a French cleat fixed with 4 screws. Total overkill because you would have trouble getting it off the wall with a crow bar.
Hard to quanitfy I know, but assuming the wall could take the load, how much weight could you reasonably expect to hold on a setup like that? It's the kind of thing I was thinking for a kilner jar rack that would probably see in excess of 100kg of static load.
Tough one. Wouldn't like to say without looking at all the variables. There are some fixings which give weight ratings, it still depends on substrate though. The shear force of a 5.5mm screw is going to be over 50kgs though.
I would start to worry around 20 kg. Probably worth having 2 screws then. I fitted one the other day must have been 25-30 kgs, it was supplied with a French cleat fixed with 4 screws. Total overkill because you would have trouble getting it off the wall with a crow bar.