BA or Metric

[nigel jones 5Participant @nigeljones5]

[nigel jones 5Participant @nigeljones5]

Cost aside, are there any physical or mechanical propties between the two which make for better use in model engineering?

[Ian S CParticipant @iansc]

I'd say, cost aside no, but with metric you have a choice of coarse and fine threads, and you can cut the thread on the lathe with out complications, with BA that's it, one pitch per size.

Ian S C

[MWParticipant @mw27036]

Yeah, well, as well as what ian said, the thread form is basically the same, but the sizes are slightly different. OBA, although closest to M6 is not m6 it's 1/4".

Michael W

[BazyleParticipant @bazyle]

BA with hex heads are readily available from 'our' suppliers in small packs. Are metric? Confess I've never looked for metric on the show stands so there may be loads.

[MWParticipant @mw27036]

I would add that for small screws in general, go with a good strength one and don't use small sizes if you don't have to, or can get away with a bigger one, as they have a tendency to strip out under force. If too little of the thread engages with the part.

Michael W

[Rufus RoughcutParticipant @rufusroughcut]

Hi chaps it's worth noting if you only won't 10 small bolts then pay show supplier prices but you should know that most fastener supply companies do sell small quantities of to anyone and would be considerably cheaper than the show prices irrespective of thread form and also they aren't cheap if you have to travel half the length of the country and pay £10 to get in to get 10 M3 or BA or 40tpi Modeng and the list goes on, or why not group purchase and by 500 to share which would be super cheap

Rufus

[JasonBModerator @jasonb]

Posted by Michael Walters on 03/09/2016 12:45:21:

Yeah, well, as well as what ian said, the thread form is basically the same, but the sizes are slightly different. OBA, although closest to M6 is not m6 it's 1/4".

Michael W

Not 1/4" unless you are doing something massively wrong, its 6.0mm dia with a 1mm pitch and 47.5deg angle

[JasonBModerator @jasonb]

Posted by Bazyle on 03/09/2016 12:47:32:

BA with hex heads are readily available from 'our' suppliers in small packs. Are metric? Confess I've never looked for metric on the show stands so there may be loads.

Yep but not as many UK suppliers do them. Bruce/polly is the only one and they buy them in from GHW in Germany who I get them from. These are all machine cut and with more suitable hex sizes.

Main problem wit buying commercial metric as suggested by Ruffus is thay look pants with forged heads, usually plated, writing etc on the heads and slack threads

 

Edited By JasonB on 03/09/2016 13:22:29

[JasonBModerator @jasonb]

Main advantage of BA if you are using imperial materials is that they fit quite nicely onto stock imperial sizes despite being a metric system. 2BA onto 3/16" stock, 5BA onto 1/8" and 7BA onto 3/32"

[Neil WyattModerator @neilwyatt]

BA fasteners look better, metric ones are cheap. For model use BA for ones that get seen

Neil

[JasonBModerator @jasonb]

Neil whats wrong with using good looking metric fasteners, not all metric ones look ugly

[MWParticipant @mw27036]

Posted by JasonB on 03/09/2016 14:01:59:

Neil whats wrong with using good looking metric fasteners, not all metric ones look ugly

Because if you're making a historic piece it gives it a more authentic feel for those who care about these things.

And yep, my bad, you're right 0BA is 6mm.

I've had some bad experiences with screws so i am a bit more picky about the type of material used, in particular i like the black High tensile regulated ones, with the knurls around the head for small sizes. 

Michael W

Edited By Michael Walters on 03/09/2016 17:20:01

[JasonBModerator @jasonb]

Michael what authentic feel do BA give over good metric fixings or for that matter good UNC over standard UNC?

[MWParticipant @mw27036]

Posted by JasonB on 03/09/2016 17:20:42:

Michael what authentic feel do BA give over good metric fixings or for that matter good UNC over standard UNC?

Well, thats up to you really but if everyone played by the rules we'd be using metric everything, so clearly people still want the older sizes for restoration or sentimentality. If something breaks thats got a 0BA thread, you get a OBA screw. Thats all there is to it, why else would people be selling them?

Michael W

[Neil WyattModerator @neilwyatt]

Posted by JasonB on 03/09/2016 14:01:59:

Neil whats wrong with using good looking metric fasteners, not all metric ones look ugly

Fine if you can find them at a sensible price!

N.

[Nick HulmeParticipant @nickhulme30114]

BA threads have metric pitches 😀

[Tim StevensParticipant @timstevens64731]

Yes, BA threads are 'metric' pitch, but they are not 'standard' in terms of the pitches used by ISO metric or French metric or German metric or Swiss metric. European thread systems tended to go up in quarters of a millimetre or quarters of tenths, eg German pitches = 0.075, 0.1, 0.125, 0.15, 0.175, 0.2 etc. In ISO metric there are a couple of 0.08, and 0.09mm, the rest being in quarters. BA, though, goes 0.1, 0.11, 0.12, 0.14, 0.15, 0.17, 0.19, 0.21mm …. And finding a thread gauge for the BA sizes seems impossible.

So, although they are measured in millimetres, that is all they tend to have in common. Even the profile of BA is special, with a steeper angle than the rest.

A full (but not complete) exposition is to be found in the Screw Thread book produced by Machinery's – mine is the 20th edition from 1972.

Cheers, Tim

[Another JohnSParticipant @anotherjohns]

Posted by Neil Wyatt on 03/09/2016 17:50:59:

Posted by JasonB on 03/09/2016 14:01:59:

Neil whats wrong with using good looking metric fasteners, not all metric ones look ugly

Fine if you can find them at a sensible price!

N.

Neil – more and more, I just make them from round rod.

I have made many like that. (price – try finding BA "inexpensive" when shipped overseas, and taps and dies – hah! Metric all the way)

When my super-duper CNC lathe comes on line, turning/threading/parting blanks will be much better, but now I just do it by the old methods. A rotary table on my CNC mill does an admirable job of making hex heads from round.

John.

[Frances IoMParticipant @francesiom58905]

John
can your CNC make cap head or grub screws in BA – luckily my local supplier stocks 2,4 + 6BA cap heads as needed 4BA cap heads to fix my Perris lathe

one of my lucky random purchases from a jumble sale turned out to be a set of BA rose bits for producing the correct size stock + a full set down to 10BA of taps + dies

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