Pattress box screw thread sizes

[clifford1]

I've just fitted a new plastic box in a plasterboard lined wall, moving the socket from it's old nearby position in a rusted metal box on a solid wall. Ready to screw the new socket onto the box I have discovered that the thread sizes are different.

Comparing the threads carefully with others around the house and those in my pot of spares I discover that 90% of them have a very slightly coarser thread. They are the same diameter as the few examples of the finer-threaded screws, but of course incompatible.

When I asked in the local shop for a pair of finer threaded screws he didn't know what I was talking about. All the ones he sold are the coarser threads, but they do not fit the new box.
What's going on here? Why aren't the threads standardised?

 

[mwatsonxx]

You probably have 4BA screws from before metrication, and now need 3.5 mm for the new box.

 

[rsgaz]

Normal ones are a metric M3.5 thread.

Very old ones are 4BA thread, which was 3.61mm major diameter and less TPI.

Couldn't tell you which year/decade it changed though, I'm sure some of the older chaps on here would know.

 

[ban-all-sheds]

Just buy a new socket.

 

[JohnW2]

Just buy a new socket.

Am I missing something, since I don't see how getting a new socket would help to solve the problem with having 4BA tapped holes in the lugs of the backbox?

To clifford1: Other than changing the box, there are two common options. Firstly, if you look around (e.g. on eBay), 4BA screws are fairly easily found. Secondly, it's often possible to re-tap the hole as M3.5 (for a 'modern' screw), using a cheap and readily-available re-threading tool (e.g. click here ), if necessary after 'squashing' the hole slightly (e.g. with strong pliers).

Kind Regards, John

 

[DetlefSchmitz]

Something is wrong with the original description. If the new back box is new, it will be M3.5, so the new screws from the shop would fit.

 

[rsgaz]

Am I missing something,

Yes, other way round, he's been trying to put 4BA screws in a new box...

new plastic box in a plasterboard lined wall, moving the socket from it's old

Just needs some screws I think. http://www.ebay.co.uk/itm/121869149783

All the ones he sold are the coarser threads, but they do not fit the new box.

Unfortunately this sounds backwards though, which had me confused initially. All the ones for sale in any DIY shop will be M3.5, which will definitely fit a new plasterboard back box, unless you have already damaged the threads when you had tried the 4BA screws.

 

[mwatsonxx]

Just buy a new socket.

And what use would that be?

You're not very good at this, are you?

 

[EFLImpudence]

He already has a new socket. The screws that came with it will fit the plaster board box.

Is the rusty box being reused? Reuse the screws?

 

[JohnW2]

Yes, other way round, he's been trying to put 4BA screws in a new box...

Ah, yes, I was missing that - so, as you say, he just needs to get some standard M3.5 screws, which are available 'anywhere'.

However, I still wonder whether I was 'missing something' (something else) in relation to BAS's comment - was he really suggesting that the OP should buy a new socket in order to get the couple of screws that would come with it?

Kind Regards, John

 

[DetlefSchmitz]

Buying a new socket, together with the screws that come with it seem eminently sensible to me, rather than reusing the donkey's years old one, from the rusty back box.

 

[ban-all-sheds]

Something is wrong with the original description. If the new back box is new, it will be M3.5, so the new screws from the shop would fit.

Likewise if he has a new socket, it will have come with M3.5 screws.

 

[JohnW2]

Buying a new socket, together with the screws that come with it seem eminently sensible to me, rather than reusing the donkey's years old one, from the rusty back box.

Probably true - but, as you have already said, there appears to be something wrong with the original description, since the OP said that he had a new socket (presumably with new screws) as well as a new back box.

Kind Regards, John

 

[ban-all-sheds]

I still wonder whether I was 'missing something' (something else) in relation to BAS's comment - was he really suggesting that the OP should buy a new socket in order to get the couple of screws that would come with it?

I've just fitted a new plastic box in a plasterboard lined wall, moving the socket from it's old nearby position in a rusted metal box on a solid wall. Ready to screw the new socket onto the box I have discovered that the thread sizes are different.

Why he said "new socket" is a puzzle, because if he had a new socket and a new box then he would not have a problem with mis-matched screws.

It seemed to me that what he was doing was taking an old socket, so old that it has BA screws, and which has been in a rusty box, i.e. somewhere damp.

So no - I wasn't suggesting replacing the socket just to get a pair of M3.5 screws, I was suggesting replacing it as it could probably do with replacing,

 

[ban-all-sheds]

Am I missing something, since I don't see how getting a new socket would help to solve the problem with having 4BA tapped holes in the lugs of the backbox?

Why would a new plastic plasterboard box have 4BA holes?