Standard backing boxes for uk electrical fittings use a non-standard metric thread - 3.5mm dia x 0.6mm pitch thread (0.6mm=>16.66 threads/cm or 42.33tpi).
Is a tap (& a die perhaps?) for this thread available from anywhere? I've just had another dud thread on a backing box to sort out & it would be useful to have one in the tool box.
TIA
How about this?
John
Why do you say non-standard? M3.5 x 0.6 is a standard size in the ISO metric coarse series - see, for example
The tap is normally availible from any electrical wholesaler
On 23 May 2006 15:34:43 -0700, "jim_in_sussex" had this to say:
B&Q stock 3.5mm taps - in the electrical section.
You can also fit a screw extender, which has a male thread one end and a female on the other. The male thread goes into the stripped hole with a
3.5mm nut on the back and your socket screws into the female part. You will need to use a shorter 3.5mm screw but they are easy to cut down.Machine Screw Extension Stud: -
Jaymack
There's them that know and them that don't know. Be very, very wary, of those who don't know, they don't know.
Draper - and others - do a tap with a plastic handle, rather like a screwdriver. My local car accessory shop - strangely - stocked them. Or try an electrical wholesaler.
You'll likely have problems getting 3.5mm nuts except by mail order for a few hundred. ;-)
They used to be sold by MK - but really offer no advantage over a long
3.5mm screw, if it's an extension you need.If you have 3.5mm nuts and a stripped thread just glue a nut onto the back of the lug.
Jaymack
In message , John McLean writes
Ah ha, thanks Jaymack. I tried to find these a while back, but find anything to do the job. I've fitted black nickel sockets etc in the kitchen, but what with tiling the matching supplied screws were too short.
Mind, the above website isn't working very well, Firefox stalls on a script, IE just keeps throwing me back to the home page.
metric tap & die set & I've never set eyes on the thread in any other context. Many thanks for the pointer.
Thanks to all posters: the stubby screwdriver style tap mentioned early on looks as if it will suit down the the ground. Many thanks.
'Non preferred' might be easier. But it's a size available in normal nuts and bolts from a decent supplier.
I suspect it was the nearest metric equivalent to the previous, imperial, size which was 4BA. [Ducks, waiting for barrage of posts pointing out that BA was specified in metric dimensions, IIRC]
Yes - obviously the clearance holes on accessories had to be compatible otherwise chaos would have reigned...
The message from John Stumbles contains these words:
BA was indeed metric. 0BA is 6mm x 1mm pitch.
4BA 3.6 x 0.66 is very close to M3.5 coarse - 3.5 x 0.6, probably close enough to get away with misuse at least once.
While BA was originally specified in metric units they are not directly interchangeable even in the apparently dimensionally equivalent sizes you mentioned. BA has a 47.5 deg thread angle and metric 60 deg.
Vaguely works one way round but not the other.
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