Back box screw

[Abyone]

Went to replace a timed switch and one of the screws to fix onto back box won't grip at all.

See photo - the hole on the right is much bigger than on left with the white insert.

At first I thought the threads had been ripped so I bought a 3.5m. threading tool but that didn't grip at all and then I tried a 4 mm bolt but that was too small also.

Anyone know what's going on - should I try a 5mm bolt or was thinking of filling with epoxy and starting again with a 3.5mm hole if I can drill and thread.

Any other suggestions?

 

[CountryFan]

It looks to me like it’s missing the brass/metal threaded retaining part.

 

[Abyone]

It looks to me like it’s missing the brass/metal threaded retaining part.

Do you mean there is an insert to go into or over that hole ?
Can I purchase something to do this ?

 

[JohnW2]

Do you mean there is an insert to go into or over that hole ?

I presume he means that the brass insert (with a thread to take a 3.5mm screw) is missing from the right hand hole in the plastic.

Can I purchase something to do this ?

I would presume not- although it would represent a bit of work, the 'obvious' solution would be to replace the entire back box. It's a rather unusual situation (and unusual box), since it seems to be a 'surface' one which has been sunk into the wall for 'flush' use.

I suppose you might be able to extract a similar insert by destroying a similar box, and then somehow getting and sticking it into the whole, but if you had another box to do that with, it would presumably make more sense to just replace the box!

Did that insert perhaps pull out when you removed the old switch (and maybe is still attached to the screw)?

 

[CountryFan]

I presume he means that the brass insert (with a thread to take a 3.5mm screw) is missing from the right hand hole in the plastic.

Correct

Do you mean there is an insert to go into or over that hole ?
Can I purchase something to do this ?

No, there’s no insert and not something I would have thought a separate item, as per @JohnW2 - easiest is to replace the backbox.

 

[pete01]

Maybe these will work?

I've never tried them, worth a go maybe.

Back Box Repair Clip Kit 10PCS 86 Type - Professional Heavy Duty Wall Socket Fixing Tool with Adjustable Support Rods & Screw Hooks for Secure Electrical Outlet Maintenance & DIY Repairs : Amazon.co.uk: DIY & Tools

Back Box Repair Clip Kit 10PCS 86 Type - Professional Heavy Duty Wall Socket Fixing Tool with Adjustable Support Rods & Screw Hooks for Secure Electrical Outlet Maintenance & DIY Repairs : Amazon.co.uk: DIY & Tools

www.amazon.co.uk

 

[CountryFan]

Maybe these will work?

I've never tried them, worth a go maybe.

Back Box Repair Clip Kit 10PCS 86 Type - Professional Heavy Duty Wall Socket Fixing Tool with Adjustable Support Rods & Screw Hooks for Secure Electrical Outlet Maintenance & DIY Repairs : Amazon.co.uk: DIY & Tools

Back Box Repair Clip Kit 10PCS 86 Type - Professional Heavy Duty Wall Socket Fixing Tool with Adjustable Support Rods & Screw Hooks for Secure Electrical Outlet Maintenance & DIY Repairs : Amazon.co.uk: DIY & Tools

www.amazon.co.uk

Wow, it seems there’s quite a few aftermarket products.

 

[Abyone]

Maybe these will work?

I've never tried them, worth a go maybe.

Back Box Repair Clip Kit 10PCS 86 Type - Professional Heavy Duty Wall Socket Fixing Tool with Adjustable Support Rods & Screw Hooks for Secure Electrical Outlet Maintenance & DIY Repairs : Amazon.co.uk: DIY & Tools

Back Box Repair Clip Kit 10PCS 86 Type - Professional Heavy Duty Wall Socket Fixing Tool with Adjustable Support Rods & Screw Hooks for Secure Electrical Outlet Maintenance & DIY Repairs : Amazon.co.uk: DIY & Tools

www.amazon.co.uk

Thanks I've ordered them and will see

 

[pete01]

Thanks I've ordered them and will see

Let us know if they are any good

 

[ebee]

Like John says replacing the whole back box would be the sensible option if you can.
However I would say that wouldn`t I ? (Being an Electrician) .
The part shown by Pete I`ve never seen in real life, the only solutions I have seen and used in real life (I bought 5 and have used 2 over a 5 year period) are for metal boxes.

To that end I had previously tried to devise a clamp/pliers with a ball bearing welded on in order to squash the existing hole for reththreading, unsucessful to use - It was an attempt to emulate an old engineering trick - You have threaded a hole and its a bit oversize so put a ball bearing on it and strike with a hammer then rethread the first thread or two to size - Never to be done on anything that relies on a decent amount of thread and a very naughty thing to do in most engineering but perhap a means to an end with a bit of thin sheet metal. Anyway to achieve a result with a metal box in a wall not much chance at all. So dig out and replace.

You`ll probably find it easier with the box in your situation to use hammer and chisel to get it out completely then clean out the hole and replace it completely causing minimum of damage to decor (and cables) if you can do it safely.
You could replace it with a metal back box and do a bit of filling in carefully unless decor is not a problem. (and you can make a hole to safely line up and not cause cable damage).

A fiddly job whatever option - You mind find a fingerplate to cover up around the backbox hole a better option too.

 

[robinbanks]

Last time I had this problem I took the rough route of cutting down a wood screw to length and grinding the head smaller. Pete’s suggestion looks great, though you might need to shave/drill out the existing plastic lump down some..

 

[JohnW2]

.... To that end I had previously tried to devise a clamp/pliers with a ball bearing welded on in order to squash the existing hole for reththreading, unsucessful to use - It was an attempt to emulate an old engineering trick - You have threaded a hole and its a bit oversize so put a ball bearing on it and strike with a hammer then rethread the first thread or two to size ....

In the case of a damaged metal lug on a metal box, my experience is that the 'lower-tech' approach of simply squeezing the lug with meaty pliers (thereby making the hole in it slightly oval) followed by re-tapping often works, as sometimes does robin's suggestion of using a modified wood screw . However, neither that nor you approach is appropriate for the OP's plastic box

.... Anyway to achieve a result with a metal box in a wall not much chance at all.

Do you perhaps mean "with a non-metal box..." ? If not, I'm not sure what point you're making!

Kind Regards, John

 

[Ragnar_AT]

You can buy threaded brass inserts that are meant to be melted into thermoplastic materials but I suppose they could be epoxied into any other material. I‘ve used them to build an acrylic case for a tablet, just drilled slightly undersized holes and pushed the brass inserts in with a hot soldering iron.

 

[JohnW2]

Last time I had this problem I took the rough route of cutting down a wood screw to length and grinding the head smaller.

I've also done that in my time with metal boxes, if simply 'squashing the lug and re-tapping' did not do the trick, and also with plastic boxes whose brass insert had a stripped thread and could not be satisfactorily re-tapped - but I don't think I'd expect it to be likely to work with the OP's plastic box (with a missing brass uinsert).

The OP's problem seems to be that the brass insert with a 3.5mm hole has come out of the hole in the plastic (and been 'lost'). If his box is made of the usual (very hard and brittle) urea-formaldehyde resin, then I would rather doubt that a wood screw would significantly 'bite into it' or, if it tried to 'bite', could well shatter the plastic ?

However it sounds as if you have done this satisfactorily - was that with a plastic box that had lost it's metal insert?

 

[JohnW2]

You can buy threaded brass inserts that are meant to be melted into thermoplastic materials but I suppose they could be epoxied into any other material.

Oh, I'd rather assumed that such would be difficult (or impossible) to find - but, if they are readily available, as you say they could presumably be epoxied into the hole in the plastic (after a bit of drilling, if necessary).

However, given how cheap back boxes are, I would have to wonder what it would cost to buy the minimum buyable quantity of inserts?