Threaded backbox

[j_s]

We've got new double socket face plates in a newly refurbished room. Unfortunately, one of the backbox screw holes is threaded and so screws just pop out when trying to tighten them up. I assume I can re-tap it, what I need to know is what with and what screw to get afterwards. Links to items would be awesome.

 

Many thanks

James

[Jeremy Harris]

The standard screws are M3.5 x 0.6.  You can buy the tap as a hand-held re-threading tool from pretty much electrical store.  Often it is the screws that the thread fails on, as they are brass, which is softer than the steel tab in the back box.  Always a good idea to run the re-threading tap through any screws that seem to be binding, as continuing to try and tighten them inevitable buggers up the screw.

[MikeSharp01]

As @JSHarris says but I have, in the past, squeezed the metal tab to close up the hole a bit before re-threading as this often helps if the hole is striped of its thread, twisting the tab can also help although it gets to be a bit more of a bodge!

[j_s]

Thanks guys, I've tried a different new screw and it's the same so I'll head to Screwfix tonight and pick up a rethreading tool along with a pack of screws as we've got another 4 rooms to deal with yet so I think I may find more as I go

[Jeremy Harris]

19 minutes ago, j_s said:

Thanks guys, I've tried a different new screw and it's the same so I'll head to Screwfix tonight and pick up a rethreading tool along with a pack of screws as we've got another 4 rooms to deal with yet so I think I may find more as I go

 

I had a batch of about 8 back boxes that had really tight threads.  Not sure why, but they all needed re-threading.  I found having boxes of different length screws to be very handy - all our back boxes are set so they only project into the plasterboard by a couple of mm, so most of the short screws that came with the faceplates were just too short.  The downside is you end up with loads of screws left over - I must have around a hundred various length ones sitting in the spares box.

[j_s]

Well ****. Rethreaded it but it turns out there must have been a slightly larger screw there before. The screw just pushes right through. What can I do now? Freshly plastered so can't change the backbox now. I wish i changed them all when the plasterboard was off!

[Jeremy Harris]

You might get away with trying an M4 countersunk screw.  The hole would need to be tapped out to M4, but with luck an M4 tap should work OK in the existing hole without drilling it out. 

[Onoff]

You might have to drill out slightly the face plate / countersink a bit deeper if using M4 screws as the heads can be bigger than M3.5 electrical screws. Otherading tools are available: 

 

https://cpc.farnell.com/draper-tools/37924/rethreading-tool-m4-0-x-0-7/dp/TL04580

 

Crap pic but I Sharpie the back of the box if I do it so the next person is aware:

 

[j_s]

Cheers guys.

 

I was going to give ptfe tape wrapped around the screw a go just as a hail mary before buying yet more stuff, think it's worth a go?

[Onoff]

7 hours ago, j_s said:

Cheers guys.

 

I was going to give ptfe tape wrapped around the screw a go just as a hail mary before buying yet more stuff, think it's worth a go?

 

No. 

 

Bodger!

 

 

[j_s]

Ok, m4 rethreading tool ordered and M4 screws. 

One other issue I had was the floating screwhole in the backbox (adjustable), the tabs that hold the piece in are open so it won't hold the adjustable bit. I've taped it for now with some airtight tape as that's the stickiest I have just to allow me to temporarily screw the face plate on as we have family staying in that room from tomorrow night and I'm away later today until tomorrow night.

 

The adjustable side isn't threaded so it's holding tight, obviously the other side is nackered but it's better than the face plate completely away from the wall and bare wire visible/touchable

[Onoff]

Post a picture? Knock the tabs back over?

[j_s]

Will do, after the family have visited and I can properly work on it next week with the re-rethreading and larger screws.