Hollow wall fixing which leaves the screw proud of the wall

...and as if by magic (or something) the moment I posted the question I discovered the answer: hollow wall anchor bolts, rather bafflingly also called Molly bolts, which are designed expressly to do what I need.

Could you put a collar or spacer on the screw, so it is done up tight but just with the collar occupying the top inch of the screw?

I have 3U of rack mounted vertically using something like this:

Theo

Surely straightforward plastic plugs and screws will be plenty strong enough to support a network swithch. It's how I always do this and I've had no problems. In fact I've supported much heavier things on plugs in plasterboard.

That's interesting, thanks. I'd have thought there'd be a tendency for the plug to turn in its hole as the screw was inserted.

Thanks for that. You might now have seen my followup post about hollow wall anchors which seem ideal for my purpose, but that bracket is something that could well be useful in the future.

Not if you make them a reasonably snug fit in the hole, most have ridges down the sides to stop them turning.

OK, thanks. I'll give it a go.

A trick I learnt is that if you can provide a relatively sealed space behind the board, injection with car body filler makes a massively loads bearing material to drill and screw into.

-- If you tell a lie big enough and keep repeating it, people will eventually come to believe it. The lie can be maintained only for such time as the State can shield the people from the political, economic and/or military consequences of the lie. It thus becomes vitally important for the State to use all of its powers to repress dissent, for the truth is the mortal enemy of the lie, and thus by extension, the truth is the greatest enemy of the State.

Joseph Goebbels

That's not reallly possible in my case, the space behind the plasterboard being sealed but also large. And anyway, the item to be hung is pretty lightweight, fortunately.

If standard wall plugs can be persuaded not to revolve (and in an extreme, they could always be glued in place, I suppose) then they will be more than adequate.

you might then try rivnuts?

That name was new to me, so thanks for the suggestion. Looking them up, they seem to be in essence metal versions of plastic plugs with an internal screw thread. I don't think they would offer any particular advantage.

Look for GripIt fixings, there are videos shoing how to fit them, you could probably pack the bolt with a stack of washers to leave the head proud?

Thanks for the thought, but I feel they're slightly overkill for this particular job. The switch to be hung isn't at all heavy and my first approach is going to be using simple plastic wall plugs with the screw left proud.

If that proves unsatisfactory I'll use the same holes with something a little more substantial.

Consider also something like one (or two) of these:

Only that you can drive the screw fully home to 'set' the anchor in place - and then back off the screw to the position you want it to be in. A plastic anchor might spring back to its original shape when you slacken off the screw, whilst a metal anchor will hold its (expanded) shape.

That's a good point, thanks. I'll try plastic plugs first, and if they do lose their grip I'll either glue them in place (which might not work if the screw isn't being gripped) or move on to one of the suggested alternatives.

Thanks.

How is the item mounted on the wall? If it is via a keyhole shaped hole on then back of the unit that fits over a screw head with the screw not fully into the wall you will be limited by the size of the screw head. In my experience many items that can be mounted this way require much smaller screws than you first estimate (small screw head = small diameter screw shank).