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Are there any published Torque settings for BA

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Michael Edwards 101/06/2020 14:34:27
59 forum posts
46 photos

Is there any published torque settings for BA nuts and bolts.

I recently tapped the cylinder for the Stuart S50 and when i put the bolts in I only done them by finger tight as I was scared to strip the threads in cast iron.

lfoggy01/06/2020 15:31:31
159 forum posts
10 photos

I've never seen or heard of any torque settings for small BA fasteners and I've never come across a torque wrench that has a suitable low range either. I'm sure these things exist but probably not really necessary. A firm 'finger tight' with a BA spanner should be OK. The threads are stronger than you think....

Lainchy01/06/2020 15:49:32
271 forum posts
103 photos

I just nipped them up with a small spanner Mike, don't go barmy though.

magpie01/06/2020 16:35:05
477 forum posts
92 photos

Small torque screwdrivers are available for use with quarter drive sockets. I have two that were given to me many years ago. They were brand new still in the boxes and made in the USA. I have never needed to use them.


Michael Gilligan01/06/2020 17:29:50
18325 forum posts
872 photos
Posted by magpie on 01/06/2020 16:35:05:

Small torque screwdrivers are available for use with quarter drive sockets. […]


Britool does [previously did ?] a nice one

Rarely used, but great ‘pose value’

angel MichaelG.


See Post #154 here:

Edited By Michael Gilligan on 01/06/2020 17:30:52

Samsaranda01/06/2020 17:55:25
1140 forum posts
5 photos

I think half a gnat’s is probably all that is required. 😇.
Dave W

old mart01/06/2020 18:06:59
3185 forum posts
201 photos

It depends how deep the threads are in the cast iron. If you can manage 4 diameters, there is very little chance of it stripping before the screw breaks.

J Hancock01/06/2020 18:24:40
647 forum posts

This may seem strange but you really need to strip/break some and learn.

Obviously not in your prized Stuart !

EdH01/06/2020 19:25:19
45 forum posts
27 photos

In the "Model Engineers Handbook" by Tubal Cain (pages 152 or later editions 13.9) there is a table giving the safe load in screws and bolts covering 0-16BA and 5/8" Whitworth down to 1/8"x40.

If you are not well practiced in tightening nuts and bolts etc then making up a practice piece and testing till destruction will give you a "feel" for when a fastener is tight enough or over tight and starting to fail.

I've had over 60 years experience with small nuts and bolts starting with Meccano in the 50's and you can definitely get a feel for how tight it should be. The right tool for the job makes a difference as well.

Michael Edwards 102/06/2020 11:15:12
59 forum posts
46 photos

Thanks all. I will start doing some tests to get a feel for stripping them.

EdH, you are correct i've just found that book on the shelf and having a read now. Forgot I even had that. Im sure that came free a one of my subscriptions to MEW. Should really be my bible so now its been promoted from the shelf to my desk.



not done it yet02/06/2020 11:27:49
6078 forum posts
20 photos

I would think the torque is likely according to material and core diameter. Nothing more. Just get more clamping force, for the finer threads (where there is a a choice of pitch), for a given torque.

JasonB02/06/2020 13:00:20
20880 forum posts
2318 photos
1 articles

Your chosen tapping drill will also have quite an affect at those small sizes, the CI could go before the screw/bolt fails.

old mart02/06/2020 14:44:37
3185 forum posts
201 photos

I used to give the apprentices metal to tap in different sizes for them to screw in bolts until they broke, or the thread stripped. It was a very educational task, and quite popular with the lads.

J BENNETT 102/06/2020 15:42:49
55 forum posts

Sometimes feel is better than a torque wrench. A while ago I was replacing the gas re-circulation valve on my Vauxhall diesel engine. Smallish bolts into alloy, so I thought better get the low range torque wrench and set the correct value. Start torquing up and its feeling pretty tight but keep going a bit more expecting the click at any moment and then the thread starts to fail. Left it there and did the other three by feel.

However, when tightening suspension components I would still always use a torque wrench as some of them have to be very tight and that is difficult to do by feel.

Neil Wyatt02/06/2020 17:29:28
18668 forum posts
727 photos
79 articles

0Ba should be similar to M6, as it is same pitch and diameter.

duncan webster02/06/2020 17:56:22
3354 forum posts
61 photos

Tightening torque is a bit of a minefield. Any stressmen look away now! Most of the tightening torque goes in to rotating the threads together and the head on its mating surface, so tightening torque is a pretty poor way of doing it. Slight change in friction throws it all out. By far the best is to measure the actual extension of the bolts, but you can't do that easily with a bolt in a blind hole. What can be done then is to drill a blind hole from the head end and measure stretch with a depth mike, but you aren't going to achieve that with a 6 ba bolt. Best suggestion I have is to look up the recommended torque for a similar sized caphead, then scale it for the different proof stress and core diameter (cubed I think). There are on line calculators, however as we don't know what the material properties of ba bolts are, that might be only a bit better than a guess. A others have said, best to develop feel for it. When I first started working in real industry design office (many years ago!) we were not allowed to use bolts less than 5/8" BSW. Why asks I? Because some under trained fitter is less likely to overtighten it was the answer. When I had the head off my car, the instructions were to put the bolts in to a fairly low torque setting, just to settle everything down, then to give them a further 1.5 truns (from memory). This puts a determined stretch in, but was a bit buttock clenching, I expected it to go bang at any moment

As regards tapping hole size, if it fails by stripping the thread, it fails along a line (cylinder actually) where the shear strength of the bolt equals the shear strength of the female. As the bolt is usually stronger than the female, drilling a slightly larger tapping hole doesn't make a lot of difference, but there are limits. I suspect ba steel bolts are made from EN1A, so you can't go too far down this road, but Tubal Cain (the British one) recommended somewhat bigger tapping holes than many, and he really did know what he was about. If the bolt fails by snapping at the core diameter, taping hole size won't make any difference at all

Clive Foster02/06/2020 17:59:06
2735 forum posts
100 photos
Posted by Neil Wyatt on 02/06/2020 17:29:28:

0Ba should be similar to M6, as it is same pitch and diameter.

Yep according to Tubal Cain 144 lb inches as opposed to 142 lb inches. But who will notice.

For all practical purposes steel BA and small metric can use same torque settings.

Interestingly he gives only 108 lb inches for 1/4 Whitworth. Presumably due to the core diameter being around 3/4 of 0BA. The ratio of core areas being very similar to the ratio of torque.

I guess thats further proof that the design intention is that the bolt should always fail before a good thread in the same material. Reality often being different.

That said 0 BA is not a size to keep in stock. It screws in, loosely, to 1/4 BSF, 1/4 UNF and M6 making a weak joint that is prone to undo at the slightest provocation.

I know we all know better but I've got to the stage of wondering why the spanner didn't fit before realising "Stupid, dangerous, mistake about to happen.".

Can take a few years before you finally admit just how effective "want to get this done tonight" and "this is the only one I have so I'll use it" can be at turning the rational part of your brain off.


Nicholas Wheeler 102/06/2020 20:19:21
642 forum posts
46 photos

My experience is that anyone who hasn't frequently used a torque wrench on small bolts(say M8 or less) is massively overtightening them!

Howard Lewis02/06/2020 22:24:02
5036 forum posts
13 photos

I used to break 1/4 BSW bolts until I began to recognise the fastener going into yield, Often too late.

Strangely, many years later, I spent six months commissioning the, at the time, worlds largest yield tightening machine. It put 32 W range 1/2 UNF bolts just in to yield Only took 6 seconds, Awesome!

One of my Designer colleagues, I am sure laid out the calculations for bolt toques, but I can't find the folder, so I'll ask him if he can let me have a copy.

I have found a paper giving an "An Analysis of Bolt Torquing"; by Clement Rajendra.

Try Googling "PDHonline Course 149 (2PDH)"

Skimming through it, it appears to concentrate on UNC, but no doubt by modifying thread angles and pitches in the calculations, figures for BA can be found.


Michael Edwards 103/06/2020 10:49:18
59 forum posts
46 photos

Gents thank you for your time and knowledge on this thread it has been really interesting reading.



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