new metal back box sunken into wall.... wall plastered..... screw thread missing in side lug when trying to screw new socket to the wall.... what to do?

You will be able to pick up a m3.5 hand tap from any electrical wholesaler...

e.g.

just run it through the hole to create a thread.

Yes, a 3.5 mm tap to cut a thread in the hole. Any electrical wholesaler should have 'em, not seen in DIY sheds.

Unless of course the hole is already bigger than a 3.5 tap. Then you have to glue a new lug behind the old one. Or if it is the adjustable lug then you can usually swap it with one from another backbox.

Depends if you have room to temp glue a nut behind the lug where the thread has gone, I suppose. It would cause some concern when you try to get the screw out some years down the line though. I have done this, and it worked, but I have to admit it was a bodge. Grin. Brian

I bodged a tapped hole in the back of the box (light switch) with a longer screw to reach. The existing lug hole was too large and I couldn't glue a nut to the back of it for some reason I forget.

Or enlarge the hole a bit to take a nutsert (insert)...

Or use a M4 rethreader and M4 screw.

Fix it with one screw and hold the other screw in with blutack to be cosmetic.

Then remember not to use that socket in case it's wobbly.

Of course if you're a professional electrician working in someone else's kitchen you can superglue the socket to the plaster.

Owain

/ Of course if you're a professional electrician working in someone else's kitchen you can superglue the socket to the plaster.

Owain/q

Not forgetting to superglue the screw in place too....

Oh and "forget" to finish the bonding to kitchen sink copper pipework, after threading 20m of single through a difficult crawl space, then test "everything" & sign it all off.....

Jim K

A few years ago when I re-did my kitchen, I was hacking off some plaster and encountered a solitary earth cable running across a wall, it was heading towards the water stopcock via a 6' gap where the kitchen extension had been build - I chipped away enough to confirm that yep, angle grinder clean through the cable at both ends, presumably the builders retrieved and "hid" the middle section of cable to avoid any awkward questions ... thankfully it wasn't difficult to find another route under stairs, across the landing and down by the soil stack to reach the stopcock.

I saw some sockets in a kitchen the other day that were siliconed into place. Perhaps this was why...

Sir - Did you suggest a reasonable and simple solution not involving:

a) Angle grinder;

b) Unusual technology;

c) Unusual but expensive tools;

Once I couldnt use an M3.5 tap to sort it, I forget why, and just used a woodscrew of exactly the right diameter. The screwheads dont look quite right though.

NT

You forgot car body filler - although to be fair that might actually work!

I've "got away" with a stripped 3.5 thread by finding a slightly larger self tapping screw from my large collection.

That would be a bodge I couldn't live with.

Using a mole wrench to slightly crush the hole (oval) and then running the tap through it may work if the hole is already oversized.

I have another way. It depends on the depth of the back box and how slim your fingers are. Remove an adjustable lug from a spare back box and just hold it in place behind the knackered lug until the 3.5 screw bites the "spare" adjustable lug.