BA versus metric reduced-head fastenings

I'm currently working on a 5" gauge loco - well, to be more accurate, just started on...

I've been thinking about fastenings, and the use of reduced-head BA nuts and bolts as seems to be widely suggested. What I'm wondering at the moment is whether or not I should use reduced-head metric fastenings instead, now available from at least one ME advertiser. This project is going to keep me going for a few years yet - would I be painting myself into a corner if I start using BA now? I've been using BA and BSF for many years now, but my last significant project - CNC router - uses only metric fasteners which are easy to get hold of. I needed to replace some bolts on my elderly Smart and Brown lathe and it wasn't as easy as it might have been to find the necessary BSF sizes, and I can only imagine that this situation will get worse.

Interested to hear other views!

The last 7 engines that I have designed and made have all used the smaller hex metric fixings and teh whole engines have been done in metric. I tend to buy mine direct from GHW in Germany who Polly/Bruce get them from as they do a larger range.

I've also done another two engines that had been started with metric fixings but as most of these were larger than whats available from GHW I made my own nuts and a few bolts with smaller than standard hex sizes

The BA hex material is getting harder to find so you may well find that those BA fasteners actually have a metric hex to them anyway.

Edited By JasonB on 26/04/2018 20:03:25

Your chances of getting widest range of less expensive fasteners and tools going forward would be metric. There are a few suppliers in Holland and Germany that do metric scale appearance nuts and screws for example, and metric studding, taps and dies are available worldwide from many suppliers.

There are still lots of model maker BA fastener users in the world, but relatively few BA fastener and tooling suppliers left, and they are mostly in UK. I'm sure if you wanted enough volume of some BA fasteners or tools you could get them done in Asia, shops there will make ANYTHING you want but the min order value would likely be in the 5,000 UK pound price range.

Thanks for the comments. It's good to know that these look OK on a model. Threads in the metric range are a bit coarser than the equivalent BA but certainly for the locations I'm looking at on a tender that should be OK - plenty of thread engagement, or I'm using nuts anyway. Thanks also to the pointer to GHW - their English is significantly better than my German, although there are a few areas that need a bit of interpretation! However, they do have a useful range of smaller sizes (anyone for M1.6 allen cap screws?). Looks like I might be ordering soon - I already have a few M2/M2.5 taps on order to go with them.

Always amuses me when I see the BA series described as non metric. The whole definition is metric - not one bit of imperial in it. It's just not an 'M' series thread.

The pitch of BA thread n in mm is P = 0.9^n rounded to 2dp. The major diameter is 6 * P^1.2. The head size is 1.75 x major diameter. ( **LINK** .).  .

Regards,

Richard.

Edited to get rid of spurious emoticon

Edited By richardandtracy on 27/04/2018 11:24:52

Richard - I agree completely with you, but it's a bit clumsy to talk about "the first metric thread system" and "the second metric thread system"! Sometimes it's just easier to go with common convention. Personally, I have no particular axe to grind one way or the other - I'm really happy that both lathe and vertical mill have DROs that switch between metric and imperial units, so I can mix systems even when working on a single piece of work. The only issue is whether there are fixings in any of the systems that combine diameter/pitch/head size etc that work in a given situation. I don't know what is used commercially these days in the situations for which the BA threads were defined.

As an aside, I love it that the Americans are so wedded to an "imperial" system!

JasonB Have you got a website address for GHW I can't find them on Internet. Thanks

Here you are ​Old School.....https://ghw-modellbau.de/index.php?cPath=4&MODsid=d48c7de78d0c614d5ffab9db62586279 Trevor

Richard and/or Tracy brings up a good point about BA and metric.

Three things here - can anyone correct/comment?

--

1) There seems to have been a bunch of metric standards, now ISO standards have taken over.

Two "for instances" M2.3 and M2.6 have been replaced with M2.5, and (if I remember this correctly) 10BA is "equivalent" to M1.7, which one might find on an Aster Gauge 1 locomotive produced in Japan, for instance.

2) Nealeb: I went from BA to ISO metric a long while ago, and I'll not be going back. Where I've lived, BA taps and dies and nuts and bolts and screws had to be ordered in from Britain, while metric was available off the shelf. Nothing wrong with BA, just availability, and I doubt it'll get better.

3) I seem to remember reading somewhere that BA taps and dies that are on-sale to Model Engineers are actually war-surplus stock. I don't know whether this has any truth in it or not, but I'd expect that industry would not have been purchasing much in the way of BA for a couple of decades, so where is the BA stuff coming from?