Screw size - UK Vintage Radio Repair and Restoration Discussion Forum

kings · 12th Nov 2010, 7:14 pm

Could anyone help me with the size and type of thread on the pair of chrome headed set screws which hold the call exchange plate onto 300 series bakelite telephones.
Many Thanks.

Herald1360 · 12th Nov 2010, 11:37 pm

If it's a "strange" thread, it's possibly an odd numbered BA size.

Mike Phelan · 13th Nov 2010, 10:14 am

Can you measure the diameter and thread pitch? Small British things are usually BA, despite the fact that's a metric system.

kings · 14th Nov 2010, 12:41 pm

Can't measure it get a correct size I will go to my local hardware store and try and get the size by trial and error.

Station X · 14th Nov 2010, 1:16 pm

You won't be able to get BA screws at a local hardware store unless it's a good old fashioned one. Even then I doubt they have odd sizes. BA fasteners have to be obtained from specialist suppliers.

Try inserting the blunt end of twist drills into the female thread to see which is the closest fit. This may enable us to determine the thread size for you.

M0TGX Terry · 14th Nov 2010, 1:38 pm

Not very widely known nowadays, but the metal cap on the top of a car's spark plug unscrews to reveal a 3BA threaded stud. (this trick is recommended by owners of E93A Ford sidevalve engines to remove the pin which holds the distributor drive shaft in place - it has a 3BA tapped hole in it)
Just a thought. Might identify the thread.
Terry

julie_m · 14th Nov 2010, 1:46 pm

Almost any fasteners you can buy nowadays will be BSM, which are directly interchangeable with DIN threads.

How sacrilegeous would it be to re-tap the old holes with a modern thread?

M0FYA Andy · 14th Nov 2010, 3:40 pm

If it is a BA thread, why retap with anything else? BA screws (including the odd-numbered sizes) are easily available from many sources, albeit not the local hardware shop. They are used extensively by model engineers.

Andy

kings · 14th Nov 2010, 6:56 pm

Thanks to everyone especially the trick about putting in a drill for size.
My local shop has a huge box of BA sizes so off I will go in the morning.

Station X · 14th Nov 2010, 7:23 pm

Quote:

My local shop has a huge box of BA sizes

You're very lucky. The last traditional hardware shop in Ipswich closed down about six years ago, a victim to DIY "sheds on the bypass". They didn't stock odd BA sizes though. The premises now house a hairdressers.

I'm not anti metric, but in the small sizes metric threads are far too coarse for my liking. The BA system is much better.

AlanBeckett · 14th Nov 2010, 9:34 pm

Quote:

Originally Posted by Station X

I'm not anti metric, but in the small sizes metric threads are far too coarse for my liking. The BA system is much better.

Which in a way is slightly odd as BA is essentially Metric - http://en.wikipedia.org/wiki/British..._screw_threads

Station X · 15th Nov 2010, 12:26 pm

Indeed. From my point of view the advantage of BA threads is that they are based on a Geometric Progression. As the diameter gets PROGRESSIVELY smaller so does the thread pitch. It's like waving a magic wand over say a 6BA screw and shrinking it to 7BA. This is not so with metric threads. BA threads were originally based on metric dimemnsions which were converted to imperial units for use in the UK. They bear no ressemblence to modern metric threads though.

However this thread (excuse the pun) is about sourcing screws for a vintage telephone, so we'd better stay on topic.

John M0GLN · 15th Nov 2010, 12:41 pm

Quote:

Originally Posted by kings

Could anyone help me with the size and type of thread on the pair of chrome headed set screws which hold the call exchange plate onto 300 series bakelite telephones.
Many Thanks.

Are you going to BVWS North West Swap Meet at Golborne this Sunday the 21st? if you are, and you could bring either the phone or a screw, I could bring some thread gauges & a vernier or even a complete set of BA & Metric taps & dies to determine the thread size for you.

John

brenellic2000 · 15th Nov 2010, 1:56 pm

... and don't forget, there is no such thing as a 'standard' metric thread for there are almost as many variations for different applications as there are Imperial! And don't forget either that if it is a small screw, it may even be the American Model Engineering thread of which I have rarely seen taps and dies in the UK, even though it is widely used here.

Barry

AlanBeckett · 15th Nov 2010, 2:09 pm

http://www.tracytools.com/index.htm

Mike Phelan · 15th Nov 2010, 3:19 pm

Quote:

Originally Posted by brenellic2000

... and don't forget, there is no such thing as a 'standard' metric thread ...

Though there are some other metric standard threads, the only ones you are likely to come across are Coarse and Fine, which only differ by their pitch.
There are two of these standard(metric coarse and metric fine) that are widely used here in the UK.

Quote:

And don't forget either that if it is a small screw, it may even be the American Model Engineering thread of which I have rarely seen taps and dies in the UK, even though it is widely used here.

Barry

Never heard of this one, but there is a Model Engineer Thread invented here in UK and uniquely having the pitch (40 TPI) the same on all sizes.
The reason for not seeing any taps or dies is also the reason for the pitch:
Most model engineers screw-cut larger items in a lathe, and the change wheels or gearbox do not then need to be changed.

I think the original question has been well and truly answered, so before we head too far into a cross-threaded OT, I'll bolt this one up!

12th Nov 2010, 7:14 pm	#1
kings Tetrode Join Date: Feb 2004 Location: Llandudno, Conwy, UK. Posts: 92	Screw size Could anyone help me with the size and type of thread on the pair of chrome headed set screws which hold the call exchange plate onto 300 series bakelite telephones. Many Thanks.

12th Nov 2010, 11:37 pm	#2
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,536	Re: Screw size If it's a "strange" thread, it's possibly an odd numbered BA size. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

13th Nov 2010, 10:14 am	#3
Mike Phelan Dekatron Join Date: Nov 2003 Location: Near Leeds, West Yorkshire, UK Posts: 4,609	Re: Screw size Can you measure the diameter and thread pitch? Small British things are usually BA, despite the fact that's a metric system. __________________ Mike.

14th Nov 2010, 12:41 pm	#4
kings Tetrode Join Date: Feb 2004 Location: Llandudno, Conwy, UK. Posts: 92	Re: Screw size Can't measure it get a correct size I will go to my local hardware store and try and get the size by trial and error.

14th Nov 2010, 1:16 pm	#5
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,289	Re: Screw size You won't be able to get BA screws at a local hardware store unless it's a good old fashioned one. Even then I doubt they have odd sizes. BA fasteners have to be obtained from specialist suppliers. Try inserting the blunt end of twist drills into the female thread to see which is the closest fit. This may enable us to determine the thread size for you. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

14th Nov 2010, 1:38 pm	#6
M0TGX Terry Hexode Join Date: Sep 2005 Location: Grantham, Lincolnshire, UK. Posts: 262	Re: Screw size Not very widely known nowadays, but the metal cap on the top of a car's spark plug unscrews to reveal a 3BA threaded stud. (this trick is recommended by owners of E93A Ford sidevalve engines to remove the pin which holds the distributor drive shaft in place - it has a 3BA tapped hole in it) Just a thought. Might identify the thread. Terry __________________ Terry the Morganist

14th Nov 2010, 1:46 pm	#7
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Screw size Almost any fasteners you can buy nowadays will be BSM, which are directly interchangeable with DIN threads. How sacrilegeous would it be to re-tap the old holes with a modern thread? __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

14th Nov 2010, 3:40 pm	#8
M0FYA Andy Nonode Join Date: May 2007 Location: Preston, Lancashire, UK. Posts: 2,511	Re: Screw size If it is a BA thread, why retap with anything else? BA screws (including the odd-numbered sizes) are easily available from many sources, albeit not the local hardware shop. They are used extensively by model engineers. Andy

14th Nov 2010, 6:56 pm	#9
kings Tetrode Join Date: Feb 2004 Location: Llandudno, Conwy, UK. Posts: 92	Re: Screw size Thanks to everyone especially the trick about putting in a drill for size. My local shop has a huge box of BA sizes so off I will go in the morning.

15th Nov 2010, 12:26 pm	#12
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,289	Re: Screw size Indeed. From my point of view the advantage of BA threads is that they are based on a Geometric Progression. As the diameter gets PROGRESSIVELY smaller so does the thread pitch. It's like waving a magic wand over say a 6BA screw and shrinking it to 7BA. This is not so with metric threads. BA threads were originally based on metric dimemnsions which were converted to imperial units for use in the UK. They bear no ressemblence to modern metric threads though. However this thread (excuse the pun) is about sourcing screws for a vintage telephone, so we'd better stay on topic. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

15th Nov 2010, 1:56 pm	#14
brenellic2000 Octode Join Date: Aug 2006 Location: Rye, East Sussex, UK. Posts: 1,647	Re: Screw size ... and don't forget, there is no such thing as a 'standard' metric thread for there are almost as many variations for different applications as there are Imperial! And don't forget either that if it is a small screw, it may even be the American Model Engineering thread of which I have rarely seen taps and dies in the UK, even though it is widely used here. Barry

15th Nov 2010, 2:09 pm	#15
AlanBeckett Rest in Peace Join Date: Dec 2008 Location: Burton upon Trent, East Staffordshire, UK. Posts: 1,686	Re: Screw size http://www.tracytools.com/index.htm