Metric Screws and Threads

[Robin DuftonParticipant @robindufton85682]

I’ve recently made a switch over from BA to making threads in metric, half way through a model which probably isn’t the best time to start. I can’t find much mentioned on metric threads and screws in model making so no idea if this has been discussed in the past.

I’ve found M5 and M4 to be a good substitute for 2 and 3BA. 4BA I’ve been using 6mm hex and 3.5×0.6. M3 for 5BA. 5mm hex and M3 thread for 6BA, and 4.5mm hex and M2.5 for 7BA. They all seem a good match, although 4BA would be better as 1/4 yet it wouldn’t be serviceable with metric tools. Smaller than 7BA is getting in to micro screw territory and I wouldn’t want to make screws that small myself so haven’t gone any further.

Making the 4, 6 and 7BA replacement screws is getting a bit of a drag. Would there be enough people interested in switching over to screws these sizes if I asked around for someone to make batches of them. I’m not looking at selling them myself, just wanting to see if there is any other interest to make it worthwhile for someone to make and offer them.

[BazyleParticipant @bazyle]

Surely all sizes of metric screws are available since it has been rumoured that people in Germany and Italy etc make models too. Just need to find a supplier in EU who can penetrate the Brexit blocks.

[Robin DuftonParticipant @robindufton85682]

I haven’t been able to find anything as that’s why I’ve made my own so far. It’s also matching the head sizes to BA as the European screws I have found have weird tiny heads that look odd, and they aren’t available in M3.5 or are expensive. One way around import rules from the EU is to source them here.

[Nigel Graham 2Participant @nigelgraham2]

All commercially-made ISO metric fasteners, in both the Coarse (the common) and Fine ranges have their own established dimensions that seem compiled with little regard for proportions or numerical progressions, and are often rather ugly stampings; but they are not made for fine-scale model-making anyway.

Have you examined the catalogues for Emkay Screw Supplies, Model Fixings, etc? They might have something suitable but it’s a slim chance.

 

[ChrisLHParticipant @chrislh]

I’ve converted to metric half way through a project like yourself but found no difficulty sourcing threaded fasteners. Have a look at “Model Fixings” on line.

[JAParticipant @ja]

Robin

This has been discussed a few times and I am surprised JasonB has not replied (he did to a similar posting of mine a few years ago).

I am building a 5″ gauge loco of well proven design but have decided, like you, to use metric fixings. If you use what is easily available you end up using stainless steel. Depending on your thoughts this may be OK but stainless steel rivets are a ……

I have also started on a Saturday project, a true metric Stuart compound marine engine. This will not use stainless nuts, studs and screws but mild steel since it can easily be blacked. The studs and some nuts will be “home made”. However most nuts and some screws have been bought from GHW-Modellbauversand over the internet. The transactions have been totally painless and delivery have always been within two weeks.

The following tables may be of use (I am not sure of their origin but they have been published quite a few times).

As you point out 4BA is a problem. M3.5 appears to be a standard size until you ……..

I wish you every success

JA (too late at night)

[ChrisLH]

On ChrisLH Said:

I’ve converted to metric half way through a project like yourself but found no difficulty sourcing threaded fasteners. Have a look at “Model Fixings” on line.

Again, they don’t have anything that exchanges with BA. Like Nigel above says, metric DIN fasteners don’t fit with BA and don’t always look right when swapped with certain BA fasteners.

I’ve looked through all of those sites and there is nothing outside of standard metric stuff. It’s 4BA and 7BA that are the issue as M3 and M4 look awful when swapped in for these, believe me I’ve tried them. 6BA I’m personally not concerned about as I’ve not seen that much of it, in fact I don’t think I have 6BA taps and dies, but was included to fill the gap. It seems it’s best to just carry on making my own screws.

JA. It is 4BA that’s been the biggest issue for us as we use a fair few of them. M3.5 nuts are easily available and making studs is easy, it’s the screws that are the problem. We use a lot less 7BA although M2.5 still doesn’t look the same as 7BA. It’s having something that fits in the already established standard we’re using.

[Michael GilliganParticipant @michaelgilligan61133]

It may help to know that M3.5 is the modern U.K. standard size for electrical pattress  screws.

Available cheaply, albeit in head-styles that you probably don’t want !

MichaelG.

[Another JohnSParticipant @anotherjohns]

I’ve been building with metric threads since the mid ’90s. My source of “smaller head” hex fasteners from when I lived in Europe is getting low, so I now source from https://knupfer.info/shop/.

There is a shop somewhere in the north of The Netherlands, I have a link to it *somewhere* but have not (yet) ordered from them.

Normal metric screws I just get from a local (well stocked) fastener supply business.

I do purchase most taps and dies from Tracy Tools.

All for shipment across the Atlantic, so sourcing them from UK or Europe doesn’t make any difference.

JohnS.

[Alan DonovanParticipant @alandonovan54394]

Hi all.

Polly Model Engineering offer small metric screws in the range M1.2 to M4.0 in packs of 25.  Is this of any interest and/or use to you.  You can view what is available on their website.

Polly Model was originally based in Long Eaton (Nottingham), but the owners recently retired and sold the business to a Derbyshire based company.  They still trade under the name of Polly Model.

I have NO connection with this business other than a satisfied customer under the ‘old’ owners.

Hope this helps.  Alan

[JasonBModerator @jasonb]

As well as Knupfer that john mentions I use GHW who have  asimilar range of netric screws with small but tall hex machined heads and matching nuts. If you don’t want to order from Germany then Polly sell a limited range of their fixings.

This is the chart I use when deciding what to use, in the case of converting from Stuart drawings then I tend to go smaller than the chart as their 2BA fixings on engines like the beam and victorial look way too big so Iwould go M4 for those. M2.5 is a good swap for 7BA particularly with the smaller hex.

If you want to go the whole hog then get some metric fine series taps and dies to replace the ME threads too.

[Clive Brown 1Participant @clivebrown1]

In 1980 MAP, then publishers of ME, set up a working party to consider metric threads for model engineering. Apparently the results were later published by BSI, but not as a BS. Tubal Cain’s “Model Engineer’s Handbook” gives more details.  IIRC, he was one of the working party.

[Michael GilliganParticipant @michaelgilligan61133]

Further to Clive’s post:

https://knowledge.bsigroup.com/products/guidance-on-metric-screw-threads-and-fasteners-for-use-by-model-engineers?version=standard

MichaelG.

[Clive Brown 1]

On Clive Brown 1 Said:

In 1980 MAP, then publishers of ME, set up a working party to consider metric threads for model engineering. Apparently the results were later published by BSI, but not as a BS. Tubal Cain’s “Model Engineer’s Handbook” gives more details.  IIRC, he was one of the working party.

The document is BSI-BS PD 6507, which is expensive!  Probably better to buy a copy of Tubal Cain’s “Model Engineer’s Handbook”, which tabulates the needful plus almost all the other technical information required in a home workshop.

Robin hasn’t made his requirement clear.  I’m assuming he’s either making high-end models where the fixings are correctly scaled to Inspector Meticulous exhibition standards, or is building models from old plans that compromised on BA in the past, where the fixings look reasonable but aren’t actually accurately scaled.  In either case, substituting a nearby standard metric sizes may not be good enough.

In my workshop the problem doesn’t arise because I don’t make models with scale accurate fasteners, and all metric has to do is hold the thing together without looking plug ugly!  Usually aesthetics are satisfied by using studs and nuts rather than standard threads.   If better looks were essential, I’d try to modify a close match in any available system, or make one from scratch.   The need for making has got worse over the years.  When BA was a current system, it was available off-the-shelf in every size and most head styles.  Not so today, because the market has dwindled to supply only the most common replacement sizes, leaving us searching for ‘New Old Stock’.   Ditto original Whitworth.

My gut feel in the UK is people either make models to the original old plans, or build objects where standard metric fasteners are ‘good-enough’, perhaps with some fettling.   I suspect these two options make the need for properly scaled metric substitutes for BA a special case – I certainly don’t want any!   In 1980 a committee felt there would be demand for this, hence PD 6507, but in practice it rarely comes up.   Could be wrong – I’m not the sort of Model Engineer who would notice!  I don’t care about rivets, paint colour, or accurate signage either.   But I expect MEs who do care about detail go the extra mile to deliver high-end results, even if that means making fasteners from scratch rather than buying them in.

Love to know what Robin is building – any chance of some photos?  It would help focus on what’s needed.

Dave

 

 

[JAParticipant @ja]

I am not sure about Polly. They have been advertising metric nuts and screws, from Germany, for quite a few years. I added some metric nuts and screws to an order placed on Polly about two and a half years ago. All the order was delivered quickly but for the nuts and screws, they were waiting to make a large enough order with the German supplier. I was not that worried since they would invoice me for them when the parts were dispatched to me. I made the occasional enquiry about the order and the reply was always the same, as above.

I have assumed my order has died with the change of ownership. I have nothing against Polly Engineering but I have yet to use the company with the new owners.

I guess it is a question of demand and that buying small items from Germany is just as easy as from a UK company.

JA

[John HinkleyParticipant @johnhinkley26699]

The French site that I usually offer up in answer to this question also appears to have been taken over, and the home page says it’s in the process of regeneration, but still gives useful links to their extensive catalogue.  For example, their special screws page starts at the smaller end of the range with these:

https://www.metivier-modelisme.com/598-vis-tete-6-pans

These, as you can see, are in steel, but they also do a selection in stainless steel and fewer in brass.  When I first clicked on the home page, Google Translate came up and offered an English version if your French is not up to scratch.  They ain’t cheap, are they? Although the heads seem to be smaller than the average offering.

John

 

[JasonBModerator @jasonb]

I have bought from Polly at exhibitions and the labels are the same as GHW. But with the lack of shows I tend to get most of them from GHW these days and they have bigger range. Also quite reasonable for small gears.

I’ve lost count of the number of times I have posted about these type of fasteners so the question certainly comes up regularly

[Robin DuftonParticipant @robindufton85682]

I don’t really have a rigid requirement. One thing that clicked last night was that with a 2 inch TE and narrow gauge 5″ loco, BA screws don’t look too out of place even if they are a compromise and we’ve just been making our own to fill the gaps. The issue is for finer scale stuff at 5″ and 3.5″, or smaller. The next project I hoped to move on to is a SR Q1 in 5″ so would likely end up making everything on that so it looks better.

If there is an existing standard then why isn’t it used. There are 3 or 4 companies making BA screws for model makers, including reduced hex stuff, so why hasn’t one of them switched? People seem to throw up their hands about not being able to get stuff from Europe, but I’m sure if enough of us hassled one of the companies making BA screws they would make metric stuff with better scaled heads.

I’m happy to do the leg work and hassle companies, even pay for the standards for them to work from and source material if needs be, as long as there is enough demand. I just can’t do that if I don’t know specifically what it is people really need or want, or if the demand is really there, but that British Standard is a good start.

As a start for updating an existing model I’m happy to work with someone and swap out the fasteners on the Haining Ransomes I redrew in metric, and offer it for free as the castings are available from Blackgates. I know it’s a model that can be built using those drawings with no issues as we’ve built one.

[JasonBModerator @jasonb]

Worth noting that the European suppliers hex sizes don’t match what TC has in his book. So rather than go down your own route getting suppliers to make to his sizes, using what the ROW does would seem to make more sense.

TC’s suggested size sare not a lot smaller than the standard hex, for example 5.5mm AF is the usual for M3, He suggests a hardly noticeable change to 5mm. The Euro sizes are 4mm AF

A quick tot up and I must have about 30 models made with these small hex fixings by now.

Those wanting an easy life can also buy via UK ebay as GHW have a shop there. Also note that Polly sell by the bag of 25 but GHW bags have 50pc in them for not much more.

[JAParticipant @ja]

Robin

I agree with you that at some time the model engineering suppliers will need to switch due to younger modellers prefering metric. However there is great resistance. Many suppliers are small family concerns and are quite happy for it to start happening after they have sold up and retired. There is also great resistance from those older than me who feel that Whitworth and BA are far superior, for strange reasons, than metric. I was amazed at some of the comments made in a very recent topic.

I suggested, before COVID, the switch could be encouraged by Stuart starting to go metric. One respected replier commented that this would be very unlikely. This leads directly on to my Saturday project, already mentioned, a truely metric Sruart two cylinder compound marine engine. Most of the parts have been redrawn and machining started. All the fixings will be home made or GHW.

People have alway made metric models but they have been very much in the minority.

JA

[JasonBModerator @jasonb]

JA has a good point there, so many start off with a set of Stuart castings as their first project using castings and the included materials and in particular fasteners almost forces their hand to go down the imperial and BA route.

Would be nice to see them offer a metric option or even just castings with no materials for those that want to go metric.

I suspect Polly only sell the metric fasteners as Anthony Mount went metric and they sell his range of designs

My recent versions of the Real and James Combes were totally metric and not just a mathematical conversion. I’ve also got a metric Compound version of the score on the drawing board screen. If you are going to change something then may as well go the whole hog!

[Robin DuftonParticipant @robindufton85682]

That’s the thing JA, I’m 38. In 30 years time will BA kit still be available and at what point will the switch happen if it isn’t, as model engineering will still be around in 30 years time like it has survived for 150+ years so far.

Every model I’ve built, from the couple of Stuart models up to 2 inch TE and a 5″ loco, I’ve redrawn and converted to metric and the last piece of the puzzle is the fixings and fasteners. Buying the German screws is great, and it’s suggested every time like it’s what should be done, but they aren’t available in M3.5 to replace 4BA which has been a common size on the models I’ve built.

And totally agree about Stuart offering metric models. The only reason for buying BA taps and dies were to build Stuart models, as I started with a 10H, and they remained from not having a great option for metric fasteners on the larger models. But that’s changed now as I’m not going back, even if I have to make them myself.

[JasonBModerator @jasonb]

Well with 30 engines built all totally metric I have not found the need for M3.5 (4BA) on any of them so are they really needed?

 

Yes if you are going to slavishly convert size for size. No if your redrawing is a redesign to use metric stock materials.

3.5mm stock is not easy to find and it is not really a metric conversion if you resort to using 9/64th stock and theading that M3.5 which is becoming hard to find, I think EKP are about the only ones that sell it.

[Nigel Graham 2Participant @nigelgraham2]

What seems to have been missed is that BA screws are available with size-smaller heads, but what in fact are we trying to replicate? The original Whitworth hexagons, which would be right for many models, were larger than those later used so if wanting very close matches to scale surely we should compare the early proportions to what is available now.

Where the original size is uncertain, as when constructing a model to manufacturer’s drawings or other archive material, or when trying to metricate a long-established published model plan-set, one approach is to multiply the candidate fastener by the scale to assess its proportions.

This is a case where finding very old, and preferably even contemporary, engineering trade reference-books can be valuable by giving typical detail proportions of components and their fastenings; often quoted from manufacturers’ drawings.

Very early machinery often had square nuts on square-headed bolts anyway, and here we have no choice but to make the fastenings if we want correct replication.

.

Also, ironically, BA is of course metric, based on the Swiss ‘Thury’ system – although BSI describes it in inches – and its full range is by geometrical progression broken by the odd sizes becoming “non-preferred”.  It does though have very few close matches with ISO fasteners, by size, and different thread-form.

To my mind the aesthetic objection to metric fasteners is less the size (the larger the scale the less noticeable the effects anyway) than the roughly-stamped bolt-heads, with embossed numbers. I suppose if you are really worried about this you could skim the heads smooth.

It is difficult to see why BA might be thought “superior” to ISO-M screws except where scale size and appearance really are critical, and BA is the nearer. There may be some advantages in some situations, by the BA’s finer pitches.

The point about BSW and BSF of course is not some sense of “superiority” but of fidelity. If the prototype used Whitworth bolts, then in the larger scales at least, Whitworth fastenings are correct. Not only historically, because the outward appearance is not affected all that much and the function is not affected at all. Rather, the hexagons are proportional to diameter. E.g. a modern 1/4″ BSW nut and bolt will be correct for a 3/4″ or 1″ original at 3″ or 4″ scales if that used the later standards. If the prototype used the early Whitworth proportions the modern fastener will be very slightly small but still proportional to its diameter at any scale. The difficulty comes in the very limited ranges of BSW / F fasteners now made, meaning if you really want the Gold Medal having to make the things yourself.

.

When I embarked far too long ago on my steam-wagon project I started with UNF! Why? Readily-obtainable fasteners (and spanners) when BS was beginning to disappear, inch dimensions compatible with the rest of the vehicle, usefully fine pitches, consistent diameter steps (by 1/16″ from 1/4″ upwards), and very neatly-finished hexagons both proportional to diameter and usefully but not noticeably smaller than the BS equivalents. With BA sizes for 3/16″ / 2BA and below. This though was in six-inch, subsequently four-inch, scale.

.

If the ISO-M series has any real consistency in diameters and proportions I have yet to find it. The range seems to be broken into rather random sub-series interrupted by random alternative pitches. M5 for example, comes in no less than five pitches – two “Coarse” and three “Fine”!

As far as I know the ISO set is the only standard fastener range of all the common ones that is neither consistent nor proportional within itself. Although it may work industrially perhaps it is this clumsy, bureaucrat-led approach that may be the real difficulty in making our models just right.

 

[Robin DuftonParticipant @robindufton85682]

I’ve not struggled to buy it through Ebay and worse case I can use 3.5mm welding electrodes. M3 to M4 is a large transition and I prefer to keep it close to what was drawn, and I’m happy making it. It seems to be something that upsets people so I’ll go back to building my models in private and running them around my garden.

[Author]

Posts