American threads

[Maurice Cox 1Participant @mauricecox1]

B.A. equivalents of American threads.

[Maurice Cox 1Participant @mauricecox1]

I am hoping American readers of this site can help me. I have some model drawings in front of me with threads specified as “6-32, 2-56, 8-32, ” etc. Can someone please tell me what the numbers refer to, so that I can choose B.A. equivalents? In all these years of modelling, I’ve not come across this. I must lead a too sheltered life! Thanks in advance,

Coxy.

[TerrydParticipant @terryd72465]

Hi Maurice,

 

I am neither North American or sheltered but here goes as far as I understand. Unified National threads are obviously imperial sized. Below 1/4″ diameter the sizes are numbered 0 – 12 with 12 being the largest. The second number is the tpi of the thread so your example say of 6-32 means a size 6 diameter thread with 32 threads per inch. ‘Size’ 6 is 0.138″ diameter and 32 tpi is a UNC (coarse series) thread. The equivalent diameter thread of the UNF (fine) series has 40 tpi so is 6-40. There are a series of charts here.  You an use these to compare with BA tables.  It is a good idea to get Alan Mundays ‘Model Engineers Utilities from Colin Ushers site there is a mine of information about threads and much more there.

 

It is therefore the diameter which matters when substituting ‘English’ Imperial screws. As in the 6-32 (or – 40) example it is 0.138″ diameter and the nearest BA size is 4BA (a bit oversize). There is no real correlation to get exact sizes. Ironically given attitudes in USA, metric threads seem a better correlation to most popular sizes.

 

Sorry if that seems complicated but it’s not really, it’s just my rambling explanation.   I am just glad that I have gone metric and simplified the whole affair, a set of metric coarse and metric fine covers just about all of my needs. I used to have sets of UNF, UNC, BA, BSF BSW, ME plus odds and sods of specials as well as metric coarse, what a nightmare.

 

Best regards

 

Terry 

Edited By Terryd on 20/11/2011 15:48:48

Edited By Terryd on 20/11/2011 15:50:01

[Anthony KnightsParticipant @anthonyknights16741]

The sizes you have given refer to the smaller sizes in the UNC series of screw threads.

No 2 is 56 TPI, Major diameter 0.086 inch or 2.184mm.

No 6 is 32 TPI, Major diameter 0.380 inch or 3.303mm.

No 8 is 32 TPI, Major diameter 0.164 inch or 4.166mm.

 

Diameterwise, these are roughly equivalent to 8BA, 5BA and 3BA respectively.

 

Hope this helps.

regards Tony.

[NJHParticipant @njh]

Hi Maurice

I have come across this in Machinery’s handbook ( 25th edition page 1640):-

 

Coarse thread series UNC & UNCR

 

No 6 – maj dia= 0.138″, 32tpi

No.2 – maj dia= 0.086″ , 56tpi

No.8 – maj dia= 0.164″, 32tpi

 

( 4BA, 8BA and 3BA respectively ???)

 

There is more info. if you send me a pm I will attempt to scan it for you.

Hope this is what you are seeking .

 

Regards

 

Norman

 

 

Edited By NJH on 20/11/2011 15:46:48

[MikeParticipant @mike89748]

Hi Maurice:

You got me puzzled by this – I must lead a sheltered life too – but I found the answer here:

http://en.wikipedia.org/wiki/Unified_Thread_Standard

 

There’s a lot of complicated (well, to me anyway!) mathematical stuff, but also a useful table which should allow you to find the nearest BA alternative.

Good luck!

[Anthony KnightsParticipant @anthonyknights16741]

Appear to have missed the 1 from the beginning of the 6/32 size. must have been the rush to beat Terry to the post. Did get the metric size correct.

Tony

[NJHParticipant @njh]

Well Maurice that was a flurry of activity – all aiming to beat our American cousins to the draw no doubt!

 

The sad thing is though, guys, that we are sat in front of our computers getting over the Sunday lunch rather than out in our workshops spoiling metal!

 

On a positive note we have quickly reached a consensus.

 

Regards

 

Norman

 

[JasonBModerator @jasonb]

Posted twice

Edited By JasonB on 20/11/2011 17:37:37

[JasonBModerator @jasonb]

Have a look in my albums, I posted the table that I made up when the same question came up a while ago.

 

 

J

PS I was late replying due to being in the workshop

Edited By JasonB on 20/11/2011 17:36:48

[TerrydParticipant @terryd72465]

Hi All,

 

I’m afraid that the cold and damp weather put the kybosh on my workshop activities as it stirred up and aggravated an old spinal injury which I suffered as a consequence of some youthful exciting motorcycling exploits. Hence the extra armchair based activities of late. But I’ll be back there soon. Ah well, fond memories,

 

Enjoy it while you can,

 

best regards

 

T

[Terry LaneParticipant @terrylane]

That’s a well laid out chart Jason, I’ve pinched a copy to laminate for my shop – pending your permission, of course! ;

[Anthony KnightsParticipant @anthonyknights16741]

I would agree with Terry that metric is the way to go, (We will eventually have no choice anyway, as commercial supplies of imperial sizes dissapear). In my limited experience I find that often metric nuts and bolts don’t “look” quite right on a scale model. Is this because of the ratio between the AF size of the hexagon and the thickness?

 

Tony

[Terry LaneParticipant @terrylane]

I don’t think there is any real risk of the supply of BA fasteners drying up any time in the immediate future, there is enough demand (us) to endure that someone will keep making them, even if it is in smaller runs at a higher cost.

[JasonBModerator @jasonb]

The supply of BA fasteners may not dry up but the supply of BA Hex is already dry in certain sizes so some will have the nearest metric hex which is usually still smaller than the ISO hex on an equivalent metric fastener.

 

Tel if you want the actual Excel file PM me your e-mail then you can add anything else to it like hex sizes, tapping & clearance holes.

 

The other problem with going to metric fasteners is that all teh bar sizes need changing to metric as well and you can’t get metric pipe fittings unless you go to mainland Europe.

 

J

 

PS What nobody spotted that I’ve got the 1/8″ ME against 0.126″

[TerrydParticipant @terryd72465]

Hi Jason,

 

I suppose that I’m lucky in that I visit France a lot, even there much of the plumbing fittings are BSP although there is a lot of metric as well. Even the French have to service old equipment.

 

On the subject of your chart, it would be useful for us metricated types to have the 3.5 and 4.5 mm thread forms on there as they fit nicely between some of the BA sizes and the taps and dies are quite reasonable priced from such dealers as Tracy Tools. For example 3.5mm fits almost perfectly in the gap between 4 and 5BA and is almost spot on substitute for number 6 UNC threads.

 

Kind regards and thanks for sharing with us,

 

Terry

[Jeff DaymanParticipant @jeffdayman43397]

The note below was a reply I made to an enquiry about US threads last year.

 

“Just in case any newbies don’t know, there is a simple rule for UNC/UNF numbered threads. The base number 0 is .060″ OD. the numbers indicate what multiple of .013″ to add to the base dia .060” to find OD.

 

example #4-40: 4 x .013 +.060 =.112″ OD 40 TPI

 

#10-32: 10 x .013 +.060=.190″ OD 32 TPI

 

check em on yer chart if you don’t believe me…

 

easy now you know the rule eh?”

[SpurryParticipant @spurry]

Posted by JasonB on 20/11/2011 17:36:03:

Have a look in my albums, I posted the table that I made up when the same question came up a while ago.

 

Jason.

It’s a very nice chart, but as you seem to have posted it as a JPG, when saved by us poorer members with none-colour printers, the numbers are almost unreadable.

 

Pete

[JasonBModerator @jasonb]

Spurry and anyone else for that matter, PM me your e-mails and I’ll send the excel file then you can add whatever you want.

 

J

[JasonBModerator @jasonb]

Chart now updated with the other metric sizes and now in delightful pastel shades, offer still stands if anyone else wants a copy of either the original excel file or pdf. ( its easier to read if you look at it in my album)

 

[Maurice Cox 1Participant @mauricecox1]

Thanks for all the feedback gents. Problem solve. I must get out more!

Coxy

[Roderick JenkinsParticipant @roderickjenkins93242]

Jason,

 

Very useful table. Ta very much.

 

Rod

[SpurryParticipant @spurry]

Jason

The new colours are very tasteful.

Thanks for the file though.

Pete

[Sub MandrelParticipant @submandrel]

> (We will eventually have no choice anyway, as commercial supplies of imperial sizes dissapear).

Look at a Model Engineer from 20, 30, 40 years ago and you will see contributors saying the same thing over and again…

 

Neil

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