Thread size

[Tiger]

Hello
Can somebody help with the size of the cover plate fixing screws on the door catches 
4 screws on each door fit the bakerlight. Covers.
Regards
            Tim

[Ruairidh Dunford]

They are the same thread as UK mains socket covers, see here: https://www.ebay.co.uk/itm/203204876633?...j8QAvD_BwE

[Tiger]

Ruairidh
Thanks for your reply.
Socket screws are not the same very very tight can be forced but still tight.
I wondered whether the best way is to retap 3.5 mm
Regards
Tim

[Ruairidh Dunford]

I have only ever used the screws linked to above, on all the covers I have fitted over the years.

It is possible you have something different from all of these.

[Tiger]

Thanks again I think the catches may be very early.
Going to use mains socket screws as you say but will try with a 3.5 mm tap.

[Ruairidh Dunford]

Tim, see here: https://youtu.be/y8q1bfpPKzo

[John Cornforth]

Hi

Electrical fittings used to be 4BA, which works out at 3.61 mm diameter and 0.66 mm pitch (38.5 TPI)

At some point they changed to M3.5, which is 3.50 mm diameter and 0.60 mm pitch (42.3 TPI). This is close enough to be interchangeable when using the tapped thin lugs of a wall box, but you might have problems with a deeper tapped hole like a brass insert.

I used M3.5 for my lock covers after running an M3.5 tap through the holes in the lock plate.

I don't know what the original thread was, possibly 4BA or possibly 1/8 BSF which is hard to find these days.

[Colin Morgan]

Back in 2018, Gary Edwards suggested that the original thread might have been 3.5BA, after I had suggested they were 4BA.  Hadn't heard of this before.  4BA screws fitted okay to fix my covers, but the holes are fairly worn. 

Not that it matters in this case, but as I commented back then, how can we tell what was originally used?  So many items on my car have been replaced over the years with whatever was around that could be made to work.  I suppose a car like that original Ruby for sale at the moment might provide some answers, but even with that, it is hard to prove originality?