Back box threads

[PhilFromYorkshire]

Hi
I am redecorating and a number of the back boxes are plastic, despite being in solid walls. I've attached a couple of photos.

Some of the threads for screwing the face plates down are stripped (screws just span when I went to unscrew them).

Is there any way to repair them without digging the back boxes out to replace the whole thing? I've used push in tabs to replace those on metal back boxes, but I'm a bit stumped by these plastic ones.

Thanks

 

[pcaouolte]

I've got those at home. When they break I replace the back box. When I moved in some had been repaired with wood screws and one had a layer of putty around it to glue it to the wall. Neither method is satisfactory.

 

[Rodders53]

Looks like there's a square brass nut 'loose' in the RHS that one could easily "not find" with a screw , that would result in it spinning - designed to allow 'levelling' of the accessory faceplate? If there's a fixed brass insert on the other side and they've been stripped, then it's a different matter and may well need a new back box.

Steel back boxes can have the threads stripped readily enough, too.

 

[pcaouolte]

That "square brass nut" is actually a bit of pink plastic that slides up and down, it does have a nut inside it. The other side has a fixed brass insert as you said. It is possible to gently extract the pink plastic and replace the nut in it but the whole lot tends to be brittle and easy to break. I find it easier to dig the old plastic one out and replace with steel. It can be done without creating much mess as the plastic can be cut away to get the old box out.

 

[Rodders53]

The brass inserts really shouldn't be that easy to strip if using brass 3.5 mm screws.
Sadly nickel plated brass screws are harder to find nowadays, as steel is cheaper.

 

[PhilFromYorkshire]

Thanks for the tips. I'll check for the brass nuts in the morning - I had assumed they were plastic threads. Just like @pcaouolte, one of mine has been "repaired" with a wood screw.

Does anyone know what thread a face plate screw is? M3.5? Might be able to grab some replacement nuts as suggested if needed. Or as you say, I might just dig them out and replace.

Thanks again

 

[333rocky333]

3.5 for modern stuff

 

[SUNRAY]

My estimation is: that is an old installation pre 1975 or so. Until then the threads were 4BA and m3.5 may grip but more than likely the first little extra twist would strip the fraction did manage to hold.
In my opinion it would be worth trying to source some 4BA screws to try before digging out the wall.

 

[PhilFromYorkshire]

Just to update this in case anyone else has the same issue and finds this post.

There were no brass nuts in either side of the box. Both sides with plastic threads in plastic holes.

I picked up a v-coil kit (don't know if these are better, worse or any different to helicoil). It's 3.5 x 0.6 mm. Comes with the correct size drill bit, tap, coil winder tool and tang breaking tool.

Literally a 5 minute job to drill and tap the plastic and insert a coil. The kit was £25 from Amazon, but it saved me hours and a whole load of faff digging out boxes and making good. Well worth it in my opinion.

Thanks again for all the help

 

[SUNRAY]

Just to update this in case anyone else has the same issue and finds this post.

There were no brass nuts in either side of the box. Both sides with plastic threads in plastic holes.

I picked up a v-coil kit (don't know if these are better, worse or any different to helicoil). It's 3.5 x 0.6 mm. Comes with the correct size drill bit, tap, coil winder tool and tang breaking tool.

Literally a 5 minute job to drill and tap the plastic and insert a coil. The kit was £25 from Amazon, but it saved me hours and a whole load of faff digging out boxes and making good. Well worth it in my opinion.

Thanks again for all the help

A brilliant result, thanks for the update.