m3 screws

[TopTrumper]

fellas,
looking for the m3 screws that have the end like a standard screw and the top half is posi looking, they might not be called m3, come to think of it.

 

[Spark123]

What are they for?
Normal backboxes use M3.5 machine screws, are they smaller than these?

 

[TopTrumper]

they are for back boxes, but sometimes the lugs dont take normal m3, so these come in very handy. ??

 

[fattony]

All back boses are 3.5mm as far as I'm aware in the olden days the screws used were 2ba I think, you could always get yourself a 3.5mm tap and retap the thread?

 

[TopTrumper]

thanks fattony.
its not the screws that are the problem, its the old backboxes.
At present i have sorted the offending backboxes, but in future i want to have these screws..
PS, i know they exist because i have used them before.

 

[Lectrician]

If it is for standard back boxes.....

M3.5 is the standard. Nothing else.

Old school back boxes are likely to be 4BA - slightly smaller than the equiv M3.5. As said, either save 4BA screws when re-wiring old places, or re-tap the 4BA hole with an M3.5 tap - These are available at all good wholesalers.

Conduit boxes use M4 screws, and the old ones where 2BA I recall - Again, slightly smaller than todays equiv. Again, I always save the old 4BA ones where I can.

 

[JohnD]

you can still buy BA screws and they are handy to have if you work on places with old Besa boxes. Some people still have a box on the garage shelf.

 

[333rocky333]

2BA was the old conduit box size, slightly BIGGER than 4mm and nearly 5mm.
It as far as I know, was not used for backboxes , the screws would possibly not go through the fixing holes in the accesories.

 

[RF Lighting]

Socket boxes used to be 4BA (2BA was conduit boxes)

I just rethread any old boxes I come across. Much easier than faffing about looking for imperial screws.


Rethreaderer

 

[TicklyT]

BA threads are still alive and well, even if they have moved to a home for retired threads living in reduced circumstances.

A model engineering supplier can usually supply all the even number sizes, as well an the non-preferred odd number sizes.
I would go along with tapping out 4BA to the 3.5mm standard.

A tap can also help restore stripped threads in a lug. Give the lug a good squeeze with a pair of mole grips or the like, and it often deforms the hole enough to take a re-tapped thread.