BA and other threads etc - UK Vintage Radio Repair and Restoration Discussion Forum

Herald1360 · 13th Feb 2015, 9:24 pm

Quote:

Originally Posted by Trev757

So why do I have a separate set of Metric and BA box spanners if the BA set will do both?

Because the AF dimension of the nuts are not physically related to the thread size, they're just what the designer decided on.

Also, only the 0BA and M6 are nearly the same, other sizes don't match up.

G8UWM-MildMartin · 14th Feb 2015, 5:12 am

BA threads are indeed specified in metric dimensions, but I suspect the nuts were made from hexagonal bar stock with imperial (outside) dimensions, though I may well be wrong. However, I can't recall where, but I read that some current production BA nuts are made from standard metric hexagonal stock because the original sizes are no longer available.

Ed_Dinning · 14th Feb 2015, 7:59 am

Hi Gents, a look at Engineers or Machinery Handbooks(or a good Google) will reveal the vast array of thread types that are available, together with a their principal dimensions as well as the relationships between these dimensions and also the relationships to other sizes in the same series.

Ed

Alan Stepney · 14th Feb 2015, 8:45 am

Lots of thread information is at:
http://www.alanstepney.info/page8.html

Wendymott · 14th Feb 2015, 2:37 pm

Thanks Alan. Great info there. now in my fav file

ThePillenwerfer · 14th Feb 2015, 3:25 pm

There's some, probably accidental, compatibility between BA and ISO threads in that a metric screw will go in a BA hole but a BA screw won't go in a metric hole.

- Joe

GrimJosef · 14th Feb 2015, 3:59 pm

Quote:

Originally Posted by Ed_Dinning

Hi Gents, a look at Engineers or Machinery Handbooks(or a good Google) will reveal the vast array of thread types that are available ...

As someone once said "That's the beauty of standards, there are so many to choose from !"

.

Cheers,

GJ

Alan Stepney · 14th Feb 2015, 5:46 pm

BA is actually a metric system as it is based upon the Swiss Thury thread. All the British Association did, when they copied the Thury thread, was to specify it in Imperial dimensions.
The major difference between Thury / BA and todays metric threads is that the latter has a 60 degree thread angle and "sharp" (as opposed to rounded) peak and trough.

kalee20 · 15th Feb 2015, 1:19 am

Sorry, but BA screws have always been specified in metric (mm) dimensions. Although, except for 0BA (6mm dia) the sizes aren't a round number.

The next size is found by multiplying by approx. 0.9, so 1BA is 5.4mm dia, 2BA is 4.8mm dia, etc, which is a good system - similar to preferred resistor values.

The thread angle is 47.5 degrees, so although a 0BA and M6 screw have the same diameter (and the same thread pitch, as well), putting an M6 nut on a 0BA screw, or vice versa, isn't good practice.

lesmw0sec · 15th Feb 2015, 10:13 am

If I recall correctly, one advantage of BA was that the drill size down from clearance was the correct size for tapping the smaller thread.

julie_m · 15th Feb 2015, 11:21 am

Yes, BA threads were designed according to a mathematical progression so that each fastener's clearance drill was the tapping drill for the next size up, and without regard for round figures either in millimetres or in inches.

kalee20 · 15th Feb 2015, 11:26 pm

Absolutely - the only round figures are 6mm diameter, 1mm pitch, for the 0BA... and for the others the round figure is the BA number!

14th Feb 2015, 5:12 am	#2
G8UWM-MildMartin Heptode Join Date: Jan 2004 Location: Stockport, Greater Manchester, UK. Posts: 827	Re: BA and other threads etc BA threads are indeed specified in metric dimensions, but I suspect the nuts were made from hexagonal bar stock with imperial (outside) dimensions, though I may well be wrong. However, I can't recall where, but I read that some current production BA nuts are made from standard metric hexagonal stock because the original sizes are no longer available.

14th Feb 2015, 7:59 am	#3
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: BA and other threads etc Hi Gents, a look at Engineers or Machinery Handbooks(or a good Google) will reveal the vast array of thread types that are available, together with a their principal dimensions as well as the relationships between these dimensions and also the relationships to other sizes in the same series. Ed

14th Feb 2015, 8:45 am	#4
Alan Stepney Rest in Peace Join Date: Feb 2008 Location: Dorset, UK. Posts: 947	Re: BA and other threads etc Lots of thread information is at: http://www.alanstepney.info/page8.html

14th Feb 2015, 2:37 pm	#5
Wendymott Octode Join Date: Jun 2013 Location: Huddersfield, West Yorkshire, UK. Posts: 1,795	Re: BA and other threads etc Thanks Alan. Great info there. now in my fav file __________________ Should get out more. Regards Wendy G8BZY

14th Feb 2015, 3:25 pm	#6
ThePillenwerfer Octode Join Date: Mar 2011 Location: Sheffield, South Yorkshire, UK. Posts: 1,453	Re: BA and other threads etc There's some, probably accidental, compatibility between BA and ISO threads in that a metric screw will go in a BA hole but a BA screw won't go in a metric hole. - Joe __________________ "Experts are only good at one thing: explaining why something will not work!"

14th Feb 2015, 5:46 pm	#8
Alan Stepney Rest in Peace Join Date: Feb 2008 Location: Dorset, UK. Posts: 947	Re: BA and other threads etc BA is actually a metric system as it is based upon the Swiss Thury thread. All the British Association did, when they copied the Thury thread, was to specify it in Imperial dimensions. The major difference between Thury / BA and todays metric threads is that the latter has a 60 degree thread angle and "sharp" (as opposed to rounded) peak and trough.

15th Feb 2015, 1:19 am	#9
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,081	Re: BA and other threads etc Sorry, but BA screws have always been specified in metric (mm) dimensions. Although, except for 0BA (6mm dia) the sizes aren't a round number. The next size is found by multiplying by approx. 0.9, so 1BA is 5.4mm dia, 2BA is 4.8mm dia, etc, which is a good system - similar to preferred resistor values. The thread angle is 47.5 degrees, so although a 0BA and M6 screw have the same diameter (and the same thread pitch, as well), putting an M6 nut on a 0BA screw, or vice versa, isn't good practice.

15th Feb 2015, 10:13 am	#10
lesmw0sec Octode Join Date: Jul 2009 Location: Carmel, Llannerchymedd, Anglesey, UK. Posts: 1,507	Re: BA and other threads etc If I recall correctly, one advantage of BA was that the drill size down from clearance was the correct size for tapping the smaller thread.

15th Feb 2015, 11:21 am	#11
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: BA and other threads etc Yes, BA threads were designed according to a mathematical progression so that each fastener's clearance drill was the tapping drill for the next size up, and without regard for round figures either in millimetres or in inches. __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

15th Feb 2015, 11:26 pm	#12
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,081	Re: BA and other threads etc Absolutely - the only round figures are 6mm diameter, 1mm pitch, for the 0BA... and for the others the round figure is the BA number!