Watchdog.

We just finished changing our leaky rads yesterday and were amazed to find that the heavy double cast iron one that generations have sat on in the living room, was only held to the wall by 4 3/4" '8's. with washers under the heads to stop them going through the bracket holes!

So?

breaking strain on those is about a ton each

And I should think the weight of the rad plus water plus person, acting on the small area of bracket in contact with the screw, must have come perilously close to that, or more, on a number of occasions. Still, they are certainly stronger than they look!

You really are clueless. Don't you KNOW what a person weighs, or about moment arms and shear forces? Or what water weighs?

No, they are exactly as strong as they look, to someone who has spend a lifetime around mechanical things.

And has in fact lifted things weighing up to a ton with hoists and the like, and hung off a mere 1/4" piton banged into a rock face, though it aint my bag..

I spent several years testing most of the batches of screws and other metal components and raw materials in the metallurgical lab at Standard Telephones.

Let me know of any other heavy radiators you fit using 3/4" 8 screws. And let me know what the householder - and 'Watchdog' program have to say about your choice.

The screws are perfectly adequate to take the load, they won't break or shear. How ever the same may not be said for the substrate into which they are driven, that may well fail. Into Plaster/plasterboard no chance, into correctly fitting plugs in stone or hard brick would be fine.

Thank you.

If its into masonry no problems.

Wood somewhat less ideal, but if decent wood, its fine.

Spamlet seems to have less than half a clue really.

I have used screws that short to fix heavier things than a radiator into 18 mm plywood. They aren't going to come out. However they might have if I had used 1" or bigger as the threads would have no longer been in the ply. I tried pulling one out with a claw hammer but it wasn't happening and I am not an 8 stone weakling. Of course I would have used a bigger screw to avoid putting washers on as I virtually never have the correct washer when I want one.

Well it wasn't actually Spamlet wot pointed out the problem: it was the fitter who has been fitting rads and building houses for some 40 odd years and not seen anything like it in all that time. Reading all the twaddle on this has lowered my trust in uk-d-i-y, which hithertofore I would have recommended to anyone.

Plaster thickness is everything re whether this will work.

3mm hard plaster, 20mm rubbish sand-cement render, MID-expansion Fischer SX6 30mm plug - whilst a 25mm screw sounds longer, it causes mid-expansion of the plug and very weak pull-out resistance. I know, because a test-pull of a radiator fitted thus removed the plugs from the holes with screws still snugged tight up to the bracket! Now had I gone with a b@st@rd 40mm screw and things are very different, the 4- way expansion plugs are very strong. Instead I have a wall to (still) repair which unobtainium wallpaper at unobtainium price in any case.

Personally a 3/4" #8 is only good for holding a backbox still in an SX6-30 whilst the plaster goes off.

I think the old "torx-style-fibre-rawlplug" are more tolerant of short screw depth, the modern polythene type rely on interference fit without much grip, the nylon 4-way mid-expansion Fischer grip well if you use a long enough screw and a tight hole which is critical otherwise they will pull out.

And yet you could sit on it and it din't come off....

THINK about it.

UNDERSTAND moment arms shear force tensile force etc etc..

Only twaddler here was you.

And its heretofore, janitor.

Oh yes, but pull out strength is important to consider as well. Never assume plaster is strong or thin on an older house, you can end up with a plug sitting in mush yet appears fine.

Still think those fibre rawlplugs did a good job, they do not slip out so easily as their cheap polythene copies.

How much thread is left after you subtract the thickness of the washer plus the thing you are affixing? I would not like to trust it.

First of all, the fact that you dont understand the relationship between moment arm and 'pull out force' is telling.

Secondly, the plastic is as good IF the hole is of the completely correct diameter.

No screw will hold in mushy plaster, and I never ever put a screw that is to take any weight at all in plasterboard unsupported. Irresepective of length diameter or what its made of.

If the plaster is rubbish, it gets the new plaster or car body filler treatment.

If its plasterboard, it gets cut away and a noggin inserted.