I'm getting some old artex skimmed out in the hall and some of the electrical socket backboxes are of the old imperial type. I would prefer to avoid having to change the back box if I need longer screws, but I can't find anywhere that sells the old BA screws. Is there an easy solution? - I thought about trying to tap the threads, but not sure if this is likely to work.
Electrical socket imperial screws
Jul 15, 2010
17 Replies
You may be able to find a metric or Whitworth screw that is close enough. What is the approximate diameter and threads per inch?
Type Size Dia Inch TPI Dia mm Pitch mm BA 3 0.1614 34.84 4.10 0.73 M 4.5 0.177 33.87 4.5 0.75 BA 2 0.185 31.35 4.70 0.81 BSF 3/16 0.1875 32 4.76 0.79 BSW 3/16 0.1875 24 4.76 1.06 MF 5 0.197 50.80 5 0.5 M 5 0.197 31.75 5 0.8 BA 1 0.2067 28.25 5.25 0.90 BSW 7/32 0.21875 24 5.56 1.06 BSF 7/32 0.2188 28 5.56 0.91 BA 0 0.2362 25.38 6.00 1.00 MF 6 0.236 33.87 6 0.75 M 6 0.236 25.40 6 1
Namrick sell some B.A. items.
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tapping the threads is easy and works ok.
NT
Accessory screws are M3.5, I'm surprised that the OP can't find BA screws. Plenty of seller hits when googling...
OK you won't find them in the DIY sheds but I'd have thought a decent electrical wholesaler might, more likely to find a little hand held M3.5 tap though. 6BA is 0.11 inch (2.794mm) so the hole can simply be tapped out.
I think I've seen a sparks using a simple hand tool to do this.
like this
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Although quite expensive. Mine is just a 3.5mm tap, a cheap file handle and some epoxy.
Thats what I've got. No predrilling needed, just use the tap once and its done.
NT
Yup, most electrical wholesalers will sell you something like:
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I thought that this was the case, but forebore giving what might be bad advice.
many electricians carry just such a tap: I assumed it was to sort out stripped or tight threads, but maybe it is quire often necessary when working on older installations.
Mine is a tap and a large chocky block section. It was given to me mumble, mumble years ago.
Dave
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> Ian. Thanks to all who replied. I was looking for the specific domed head screws, but hadn't considered that plain BA screws would do just as well. Senior moment! May try the tap solution though as this seems to be the favoured way to go.
John Miller
Think the actual name is 'raised head' IIRC and yes, they are near impossible to find - especially in the original finish which might be chrome or bronze, etc. However a countersunk head BA one will work just fine.
The other alternative to re-tapping the threads on a steel back box is to enlarge the hole to clearance for a metric screw and superglue a nut to the back of the lug. But you won't find nuts in the average DIY place.
And connect a link between the earth terminals on the back box and the socket since the superglue means that you won't be able to rely on earth continuity through the fixing screws.
You never rely on that connection anyway. Screws can come loose. Corrosion can occur. Etc.
The regs haven't allowed that for a while. Link required from backbox to accessory.
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