BA Screws to Metric Screws

[Armando MenesesParticipant @armandomeneses27262]

Hello.
I am a beginner in model enginner, and started my first model, will need much your help.
I’ve been searching the net but still not sure.
My question today is, for example a screw 5 BA conversion to metric measurement , which will be?

I look forward to your help.
Thanks

Regards

[Armando MenesesParticipant @armandomeneses27262]

[JasonBModerator @jasonb]

The nearest metric equivalent will be M3.5 x 0.6mm. But M3x0.5 is more commonly used

 

For bolts, screws and nuts its fairly easy to just change from imperial to metric but if it were a rod with a threaded enf then the rod will need to be changed and any parts it passes through such as glands etc. For example a 1/8″ rod will typically be threaded 5BA but you can’t get an M3 die onto a 1/8″ shaft (3.175mm)  so a 3mm rod would need to be used and this is why M3 is prefered to M3.5 as you can’t easily buy 3.5mm rod

 

And before anyone else chips in the BA system is in fact metric based.

 

This table gives equivalents

 

Jason

 

Edited By JasonB on 18/06/2011 13:04:46

[Richard ParsonsParticipant @richardparsons61721]

JasonB – BAs metric! – Do not you believe it . Just before I left old England I went to a place I knew which sold BA sizes. His entire stock had been impounded by some local idiot (some sort of Trading Standard Officer) who had ruled (on the basis of a declaration by the BSI) BAs are inch – so you cannot sell them – that is official! You and I know that the base threads (O BA) is 6mm dia 1mmpitch etc, but they are still inch. I suppose that 19mm which is within 0.05mm of ¾” is also ‘inch’.

[PatParticipant @pat]

Hi Armando

 

The problems start or end with the availability of nuts – screws – taps and dies. For model work the size of the nut is also important and non standard nut sized models abound.

 

The table posted by Jason is excellent but you need to look at the industry preferred sizes as this can make a difference when purchasing tools. However for many the appearance is more important so the across flats size leads to for example a 5BA nut across flats size but with a 6BA thread.

 

So start with the appearance full size – scale down to the across flats size of the nut and make your own nuts with the most appropriate standard thread.

 

Regards – Pat

[JasonBModerator @jasonb]

Richard, I said it was metric based not a metric system, as you say 0BA being 6.0mm

 

Pat, the more commonly used is a 6BA AF nut with 5BA thread not the other way round as you say. Thats why a lot of suppliers sell “one size smaller” fixings, its the hex that is smaller not the thread

 

Jason

[Steve WithnellParticipant @stevewithnell34426]

Bit of a lark really this metric stuff. A local carpet shop sells by the 0.85 sq metre and I bought a set of metric hole saws – when I opened the box 25.4mm 50.8mm, 76.2mm, you can guess the next in the series

 

Oh and btw French markets used to sell certain foodstuffs by the pound…but it was a 12 ounce pound

 

 

 

[NobbyParticipant @nobby]

Hi

As JasonBs table shows .toolmakers use M5 for 2BA Also its the same Allen key for allen cap screws

Nobby

 

[Chris TriceParticipant @christrice43267]

The threadform of BA screws is quite different from metric. 0 BA has the same O.D. as M6 (6mm obviously) and a 1mm thread pitch but that’s where the similarity ends. The smaller BA sizes don’t match any other metric thread being literally scaled down versions of the size immediately above.

[John Stevenson 1Participant @johnstevenson1]

M5 will fit a 2BA hole if you whack it hard enough, the riveted head looks quite pleasing.

 

John S.

[TerrydParticipant @terryd72465]

Posted by Richard Parsons on 18/06/2011 16:07:49:

JasonB – BAs metric! – Do not you believe it . Just before I left old England I went to a place I knew which sold BA sizes. His entire stock had been impounded by some local idiot (some sort of Trading Standard Officer) who had ruled (on the basis of a declaration by the BSI) BAs are inch – so you cannot sell them – that is official! You and I know that the base threads (O BA) is 6mm dia 1mmpitch etc, but they are still inch. I suppose that 19mm which is within 0.05mm of ¾” is also ‘inch’.

Hi Richard,

 

It isn’t illegal to sell imperial sizes of fastenings, otherwise older instruments, machines and equipment could not be repaired or maintained. My Boxford would have died by now as would many veteran and vintage cars etc. I don’t know who the ‘local idiot’ was but it certainly wouldn’t be an official, maybe the shopkeeper who no longer stocked them? They are still being made, my local ironmonger stocks many imperial sizes and they and not on the ‘top shelf’ or ‘under the counter’. This is the stuff that urban legends are made from.

 

 

 

Posted by Steve Withnell on 18/06/2011 19:57:20:

Oh and btw French markets used to sell certain foodstuffs by the pound…but it was a 12 ounce pound

 

 

Hi Steve,

 

that is because the pound was an international measure as was the mile, but there were as many definitions as there were countries. Originally in England the pound weight was also 12 ounces but got changed to 16 somewhere along our muddled way.

 

It’s interesting to note that the French for pound is ‘livre’, from the Latin ‘libra’, which is why the imperial symbol for pound is lb and not p. Also interestingly, the £ symbol is simply a decorated L (for Libra), the cross lines (should be 2) come about because that was the medieval scribes way of denoting an abbreviation.

 

By the way, the terms ‘avoirdupois’ and ‘troy’ which we use to define our ounces are of course French definitions. We adopted these way back to prevent confusion with the many other types of ‘ounce’ used internationally.

 

Regards

 

Terry

[Armando MenesesParticipant @armandomeneses27262]

Thanks for your help.
Thanks JasonB for the table of equivalents.
But my confusion is: 5 BA is the measure of which part of the screw?
Can tell which the measures to the letter A, B and C?
Sorry to put the difficulties in this way.
I found a German store, which has a lot of screws (metric ), but it is not easy to see what all the measures. I leave here the link
The screws are for the chassis model Didcot 14XX, drawings of Mr. HN Evans. One more question, I have to use steel screws?

Armando

[Peter G. ShawParticipant @peterg-shaw75338]

Armando,

 

5BA is NOT a direct measurement of a screw. It is simply a reference to the thread form and pitch, nothing more, nothing less. Therefore if you wish to obtain the thread dimensions, then you HAVE to refer to a table.

 

From Tubal Cain’s Model Engineers Handbook, your dimension A is 0.094inch or 2.3876mm, dimension B is 0.220inch or 5.588mm and dimension C is 0.1260inch or 3.2mm.

 

5BA has a thread form of 47½° and a pitch of 0.59mm (approximate threads per inch of 43.1).

 

Hope this helps,

 

Peter G. Shaw

 

 

[Armando MenesesParticipant @armandomeneses27262]

Peter G. Shaw.

 

Thank you. I had understood the table JasonB gave the link. But I could not get an idea of ​​the measures. Thank you.

 

Armando

[PatParticipant @pat]

Armando You must be getting confused by now.

 

The BA standard is primarily a description of the thread. The outside dimensions of the nut (across flats and thickness are suggested but they can be varied depending upon the application). The head on the screw can take various forms and there are preferred sizes but again these work out too big to represent a scale model of a bigger real life size counterpart.

 

For scale models the small standard nuts and bolts are not a good match for their larger sized counterparts. Put another way magnifying a small nut and bolt to look like one 8 times the size will look very strange as it would have an across flats nut dimension that was way too big. That means that you will be looking at a standard thread and BA is common as there are cheap dies and taps in both the odd and even numbers down to 10BA. Bellow 10BA the common one is 12 BA and then you are into the watch threads but 12BA is very small!

 

As a starting point use a 5BA thread with the 6BA head sizes but I hope some one will give you a table as this is not my field other than I have done this to save weight on the odd occasion not for looks.

 

Regards – Pat

 

PS give up looking for metric or any other standard as a direct conversion as the small sizes are not scale replicas of the bigger sizes.  

 

 

Edited By Pat on 20/06/2011 16:00:19

[JasonBModerator @jasonb]

5BA will refer to the “A” part of your picture the overall dia of 5BA is 0.126″ or 3.175mm that is why an M3 thread would be the closest metric substitute, the threaded part “A” would measure 3.00mm.

 

The standard head size for M3 is 5.5mm and 5BA is a little larger but a lot of 5BA fixings are now made from 5.50mm hex as the old sizes are not available so as its for the chassis I would not bother looking for anything smaller.

 

Yes use steel.

 

Jason

Edited By JasonB on 20/06/2011 16:42:41

Edited By JasonB on 20/06/2011 16:43:04

[Armando MenesesParticipant @armandomeneses27262]

Thanks Pat.

 

 

I'll put it another way.
I'm buying, as the drawings from REEVES 2000. They have the bolt and nuts as BA. My problem is that I have drills and tools to tighten bolts and nuts are metrics, like all the rest of the tools I have. Never worked with imperial measurements and because of tools and drills, it was much easier for me to work with metric measurements. Since in relation to the drawings of the model, I have to convert to metric

Edited By Mike Poole on 21/09/2020 11:43:18

[Armando MenesesParticipant @armandomeneses27262]

I do not know what happened in the previous post, is not complete.
Again.

Thanks Pat.
I'll put it another way.
I'm buying, as the drawings, from REEVES 2000. They have the bolts and nuts as BA. My problem is the drills I have are metric and the tools to tighten bolts and nuts are also metrics, like all the rest of the tools I have. Never worked with imperial measurements and because of tools and drills, it was much easier for me to work with metric measurements.

Edited By Mike Poole on 21/09/2020 11:43:58

[JasonBModerator @jasonb]

Just substitute as follows for fixings, Metric coarse

 

10BA use M1.6

8BA use M2.2

7BA use M2.5

5BA use M3

4BA use M3.5

3BA use M4

2BA use M5

0BA use M6

 

For pipe fittings the The metric fine series is better and this is waht a lot of the european fittings are threaded with anyway if you want to use commercially made ones for example

 

1/4x40ME use M6x0.75

3/16x40ME use M5x0.5

5/32x40ME use M4x0.5

 

Edited By JasonB on 20/06/2011 17:34:39

[Armando MenesesParticipant @armandomeneses27262]

 

I do not know what happened in the two previous post, are not complete.
Shipping now missing part.

 

Since in relation to the drawings of the model, I have to convert to metric measures. When I bought the drawings before I asked if there was to metric measures, but no. What I am doing is bring the measures close possible.

 

 

In the drawings, tells I need screws BA 5, BA 6, BA 8 …. If I buy from Reeves, I get what I need?

 

 

 

 

Edited By Mike Poole on 21/09/2020 11:44:21

[Armando MenesesParticipant @armandomeneses27262]

I am not getting the post complete.
A bit more.

If you buy BA screws, the tightening tools, has to be different from metrics?

 

Armando.

Ouvir

Ler foneticamente

[JasonBModerator @jasonb]

Yes you will need different spanners or sockets as well as Taps & dies if you have to cut any threads.

 

There are some sizes that the spanner will fit both BA & Metric but not all or you risk damaging the head/nut

[Richard ParsonsParticipant @richardparsons61721]

Armando in a word yes!

If you use The American UNC/UNF threads you need inch size spanners which are in fractions of an inch AF (across the flats). If you use ISO metrics you use Metric spanners. Though some will coincide (just about) with the American (13mm is ½&#8221 etc. If you use BSW or BSF threads you need a Whitworth set of spanners.

BA spanners are special to the BA range. A No 2 BA spanner will fit the No 2 BA thread with a standard head on it. It is the thread No which determines the head size (and the spanner). You can however buy/make ‘Specials’ these are BA threads with a size (or two) smaller head. The basis of the BA system is that the thread angle is constant at 47 ½ ° but the pitch of each size is 90% of the previous size. The largest is no 0 BA which is 6mm diameter 1mm pitch. The pitch of No 1 BA is therefore 0.9mm, 2Ba is 90% of 0.9 which is 0.81 and so on down to No 24 BA which is the smallest round about 0.25 mm stock bar size. You will find the Metric tapping and clearing sizes drills for all BAs in metric here http://www.clag.org.uk/bascrew.html, but he only goes down to No 16 BA It is a good idea to select a Tapping size so for a No 4 BA tapping size I tend to choose not a 3.0mm but a 3.1 mm or even a 3.2mm drill. It is easier than trying to dig out a broken tap!

BA means The British Association for the Advancement of Science who designed the threads in co-operation with the Swiss Watchmakers’ association round about the year 1900. From 6mm down to 1mm there are 12 sizes in Metrics there are some 20 sizes for the same range. You pay your money and take your choice.

Regards

Dick Parsons

[NJHParticipant @njh]

Hi Armando

 

The seemingly huge range of BA sizes quoted by some here must be daunting if you are thinking of buying spanners and threading gear however in practice it may not be so bad. Most models (except the smallest and most intricate) will not use smaller than 10BA and most use only even sizes i.e. 2,4,6,8,10BA. Occasionaly 5BA and 7BA are encountered.

It will,of course, depend on the model you are making but in many cases 2,4,& 6 will cover the majority of fastenings. The thing is then, to look at your project and buy just the ones needed. Are you in the UK ? – if so the fixings and tools are readily available and reasonably priced – elsewhere I’m not so sure! As far as tapping and clearance drills go you don’t need imperial and most people would, I guess, use metric drills today. A set of 1mm to 6mm x 0.1 steps should cope with most of your needs for some time and just buy the larger ones as the need arises.

 

Regards

 

Norman

Edited By NJH on 20/06/2011 20:14:52

[PatParticipant @pat]

Armando – If you are constructing a scale model you can do one of two things. Spend a lot of time converting all the dimensions to their metric equivalents. It is only thickness of sheet metal and the cross section of bar material that will cause any problem of supply apart from those pesky screw fittings.

 

Reeves or any other publisher of designs will have worked out the across flats (spanner size) for the fixings. JasonB has given you information on the near metric equivalents. Unfortunately the metric coarse thread is weaker than the equivalent BA and metric fine is a better substitute. But local supply of metric screws as well as BA will hinge in the preferred sizes which means probably that 2.5 and 3.5 will not be at the local shop.

 

Check that the materials list is not giving non standard across flats size for the threads. It is normal practice to use one size down for the across flats size so that the M3 thread has an M2.5 A/F spanner. Down load the screw thread standards of the web from a google search. Here is one:-

 

http://www.colinusher.info/Livesteam/spannerdata.html

 

Regards – Pat

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