What size screw do I need for (50's) ceiling rose backbox?

[blackworx]

Replacing the ceiling roses in my house. All the lights have a metal backbox and the rose attaches with 2 brass screws, but I have managed to lose a few of the screws.

Since the house was built in the 50's I'm assuming they're not gonna be metric. Does anyone know what they're likely to be and if they're easy to get hold of?

 

[333rocky333]

Proberly a BA thread size?
Is it a round besa box then 2BA
Easy to get although stress it is 2BA you want or they will palm you off with 4mm which are too small.

 

[ColJack]

2BA..
or an M4 tap and M4 brass screws..

 

[333rocky333]

2BA..
or an M4 tap and M4 brass screws..

I recall 2ba is larger than 4mm

 

[Adam_151]

I understand that an M5 will thread into a 2BA thread, althogh the thread is cut at a different angle so the faces will not mate properly

http://www.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=29459

 

[333rocky333]

I understand that an M5 will thread into a 2BA thread, althogh the thread is cut at a different angle so the faces will not mate properly

I think it depends how thick the threaded bit is.
I have had trouble getting 5mm in besa boxes without threading them to 5mm, however old C50 boards with 4 2ba lid screws, the lid fixing threads are thinner with less turns and 5mm will fit most of the time.
I would say 5mm and 2BA is very close and dependant on the guality of thread whether they fit or not.

 

[SUNRAY]

I understand that an M5 will thread into a 2BA thread, althogh the thread is cut at a different angle so the faces will not mate properly

http://www.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=29459[/QUOTE]

It will go in but chews the brass a bit.
I run a M5 taptite screw in first to 'clean the thread' before using a brass screw

 

[Lectrician]

You can usually get 2BA pan head or cheese head screws at your good old handyman stores. Never found a wholesaler that has them.

 

[blackworx]

Wow, great response thanks! The backboxes are the round ones mentioned so I'll try to get hold of some 2BA's, but since I just now learned about taptite screws I have a backup plan that doesn't involve getting a tap and die set, cheers sunray.

 

[Lectrician]

Not ideal, but regularly done is to use a hex head self drilling self tapper.

 

[blackworx]

Managed to pick up a wee handful of 2BA's from a classic car specialist near my work, sorted, thanks all

 

[RF Lighting]

You can usually get 2BA pan head or cheese head screws at your good old handyman stores. Never found a wholesaler that has them.

Our local independant wholesaler keeps them

 

[securespark]

My local ironmonger (!!) has them:

http://www.brianpope.com/