By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by Allendale Jan 24th

Tap/Die sets - BSW/BSF or UNC/UNF?

All Topics | Latest Posts

Search for:  in Thread Title in  
IanT23/10/2020 23:50:53
1680 forum posts
163 photos
Posted by William Ayerst on 23/10/2020 13:42:22:

Good afternoon gents,

I'm starting in my model engineering journey. I have to 'pick one' to start my collection, the part I'm working on has no other interfaces so I can pick either. I would prefer not to use metric components as I have everything else in imperial.

Well, we've established that you are in the UK Bill - so that helps a fair bit.

All of my (main) machines are "Imperial" but that doesn't in any way have to dictate what thread sizes you need to use to build your models or projects. Personally, I use metric fasteners for most of my non-model work, because they are less expensive and more readily available than anything else in the UK these days. What is "non-model" work?

It's just about everything above M3 really (maybe M4) that I'm "scratch" building. The fasteners and screw-cutting tools are readily available and not that expensive. So metric fasteners are my "Goto" choice for anything in the way of jigs, tool-holders, accessories and just about anything else in my Workshop.

For my 'modelling', I use BA and ME because most of my models were either built or designed using those fittings and I've got good stocks of both BA screw tackle (& fittings) in the mid-range sizes. However, I should note that the smaller BA sizes (12, 14 & 16BA) are now becoming increasingly hard to find (and expensive). So I've started to look at the smaller metric fixings for my modelling needs in these smaller sizes.

As I own both British & American 'vintage' machinery, I have a good range of Whitworth & UNF/C screw-cutting tackle (taps & dies) but if I was starting over (from a blank page) then I would almost certainly adopt metric fasteners as my 'Standard' unless I had a very good reason not to do so.

In the UK, you will find some use for BSW and BSF but rarely UNC/F (unless you own US kit) - but Metric has been here in UK for many years now and is the way to go.



Brian H24/10/2020 08:07:12
1862 forum posts
106 photos

One problem with bought screws, nuts and bolts is the head thickness if modelling anything made before WW2.

The bolt thickness should equal the bolt diameter on anything older and will generally require a DIY approach.


larry phelan 124/10/2020 10:13:01
868 forum posts
17 photos

Would have to agree with S-O-D about how difficult it is to find Whitworth screws. I needed some recently to repair a piece of old farm machinery and found it near impossible to get any locally. Some places I went to just looked at me as if I had two heads, had no idea what I was talking about. Nothing except Metric or UNF..

I ended up making some, which did the job, a bit slow and not something you would like to have to do all the time.

On top of all that, the price of the few I did get was Mega Bucks !,seems like nobody is making them anymore.

When they went Metric over here, they went all the way.

Nigel McBurney 124/10/2020 10:29:01
762 forum posts
3 photos

Read the posts no mention of 26 tpi brass thread,very useful thread series for models and full size restoration,I have only bought two cased sets of taps and dies, in recent years a whit set up to 1/2 inch as my collection of loose whit items were wearing out after 40 odd years of use, with one snag ,the o/dia of the dies was the same rather small size,so it was easy to die a small thread with the die holder,but near impossible to cut 1/2 inch with the same die holder,next time I buy a larger die over the web I will also find what the o/dia is so that it will fit my larger and long handled die holder.My other set is a 1940 (so the inspection ticket said)ex military 1/2 to 1 inch whit tap and die,45 years old brand new covered in WD grease no rust and beautifully made in a green wood lined steel case,each die has a set up ring and guide which in turn fits into the large dieholder,so that a die can be set to cut size and can removed from the die holder without loosing the adjustment.The superb sliding block tap holder is made in polished steel and it gets used far more on driving all my other large taps than producing just whit threads ,the tap holder its self was well worth the cost of the whole set. My only regret was that I did not buy a similar BSP set offered to me at the same.So in reality its more economical to buy taps and dies as and when you want them, as for type of thread it does not really matter as long as the result looks right,the fasteners should be close to scale,

Maurice Taylor24/10/2020 10:43:59
151 forum posts
23 photos

Hi , There are plenty of Whitworth ,bsf, cycle thread bolts ,nuts etc on eBay.

Not much difference in price of similar size metric or Whitworth bolts.


Edited By Maurice Taylor on 24/10/2020 10:52:42

Andrew Johnston24/10/2020 11:57:28
5732 forum posts
660 photos

Bother, due to finger trouble I've just lost what I was typing. Just as well though as I was beginning to ramble. I can now start again with a better idea of what to say. On the plus side it's just started raining so I can abandon plans for weeding the garden and hit the workshop instead.

The OP needs to decide what he wants to make before buying taps and dies. I'm building a relatively large (4" scale) engine but the most common threads are 1/4" BSF and 2BA. Smaller engines will most likely be metric, BA or UNC/UNF depending upon where and when they were designed.

I mostly use metric threads for work related design, but my engines are a mix of metric, BA, BSP and BSF and even one part which is 5/8" UNF. Internally on my engines I use metric threads and commercial socket head bolts/screws. But for visible threads I reverted to the original BA and BSF threads after a brief period of aiming to convert everything to metric. I use commercial BA nuts and small BA screws from EKP. I understand that small scale metric fasteners are available from European suppliers. But I use so few that I make my own. I was unimpressed with commercial fasteners for the larger threads so I also make my own; 2BA bolts and M4 nuts:

2ba bolts m4 nuts.jpg

1/4" and 5/16" BSF studs:


And matching nuts:


Of course it helps that I've got a repetition lathe; once set up it's very quick to turn out multiple parts.

To summarise the ramblings; decide what to make and then buy taps and dies as needed. There are two rules for buying taps and dies, and any type of cutting tool:

Rule 1: Don't buy cheap

Rule 2: See rule 1

I buy from professional tool shops for taps and dies I use a lot. For odd sizes I won't use often I tend to buy from Ebay, but only branded names such as Dormer or LAL and from UK sellers.This is what happens to cheap tools, bought from a UK ME supplier, that were not up to standard:


They get recycled!


Paul Kemp24/10/2020 13:00:48
580 forum posts
18 photos


That is some failure on the taps? I don't think I have ever seen a tap break like that, was there a groove in the shank at point of fracture? Were you hand tapping when they broke or under power? I do have one die with a similar appearance to yours lol, I think the problem with mine was less with the die and more with the holder being oversize and allowing me to Jack the die open too far.


Henry Brown24/10/2020 13:19:04
340 forum posts
90 photos

LOL, I wish all taps broke there if they are going to Andrew!

Another good reason for buying quality taps, it's usually not so bad if a die goes other than the inconvenience of getting another...

Andrew Johnston24/10/2020 13:25:03
5732 forum posts
660 photos
Posted by Paul Kemp on 24/10/2020 13:00:48:

That is some failure on the taps? I don't think I have ever seen a tap break like that, was there a groove in the shank at point of fracture? Were you hand tapping when they broke or under power?

None of the above. I broke them deliberately (Widlarised is the technical term *) as the threads they produced simply didn't fit together properly whatever I tried. I can't remember the exact details but I got so fed up making, and scrapping, parts that didn't fit that I binned the taps and die. I then bought a 5/8" UNF spiral flute tap from a commercial supplier (probably Cutwel as the brand is YG) and screwcut the external threads. I no longer use the ME supplier from whom I orginally bought the taps and die.


* After the legendary analogue integrated circuit designer Bob Widlar. Having found a duff component during debug his advice was to smack it with a hammer, for two reasons. One, it makes you feel better, and two if you leave it lying around someone else will use it and then have to go through the same debug process.

Jeff Dayman24/10/2020 14:42:52
1915 forum posts
45 photos

Just my $0.02 worth re fastener systems for ME - if I were starting to gather tooling and fasteners for some ME activity, with a view to cost and global availability of tools / fasteners for next 10-20 years, I would go all metric all HSS tools no question. Most of the world apart from USA and UK have gone metric some time ago. The high volume manufacturing power in the far east means normal commercial metric fasteners and threadmaking tools are reasonably priced and very available.

One thing that is increasingly hard to find (anywhere) is small size steel hex stock under 5 mm a/f for nut making for steam models. If you plan to do any hex fastener making I recommend getting a stock of some small hex now. It may not be available in a few years as commercial screw production goes away from screw machine screw production and into all very high volume cold-headed fastener production of standardized screws per DIN etc. I like to use nuts and studs on steam models because a) that's what the originals used, so they look right b) if you make your own studding and nuts you save a pile of money on scale screws and bolts and nuts c) making a big pile of scale 0.8 mm thread nuts is good for building character, is very "Zen", and good for realigning your chi (life energy) pathways. smiley

William Ayerst24/10/2020 14:54:21
66 forum posts

So no 63 tooth change gear with the lathe but presumably I can buy one if required?

What brand should I be looking for, for taps and dies? Dormer? Presto?

Vic24/10/2020 14:56:20
2645 forum posts
20 photos
Posted by Jeff Dayman on 24/10/2020 14:42:52:

Most of the world apart from USA and UK have gone metric some time ago.

I don’t know where you got that idea from but the UK went metric decades ago.


It’s a darn sight easier to get metric fasteners over here but you can still get some imperial stuff, likely due to the USA still using them.

Some old folks still like to buy imperial machines for some reason rather than convert to metric but they seem to be a dying breed. Machine tool dealers don’t help either sometimes, my metric VMC mill was supplied with a Whitworth draw bar that got thrown into a cupboard never to be seen again! laugh

Vic24/10/2020 15:27:27
2645 forum posts
20 photos

Just out of interest I looked to see what imperial stuff Australia still sell and sure enough, like the UK they still sell 8’ x 4’ sheets of ply - marked in metric sizes of course! cheeky


Bill Phinn24/10/2020 18:35:24
385 forum posts
70 photos
Posted by Mike Poole on 23/10/2020 22:57:01:
Posted by Bill Phinn on 23/10/2020 22:22:57:
Posted by Mike Poole on 23/10/2020 20:41:34:

if you are making them from scratch then you can put whatever head you like on them.


A genuine question, Mike, if a little off-topic:

A large choice of head shape is clearly something any lathe can offer, but what about the "slot"? A simple line slot will surely look wrong in some situations, but what other realistic choices does the lathe owner making fasteners from scratch have? Hex, Torx, Pozi, Philips et al. are surely not practicable.

I was rather thinking of getting the proportions of a hex head to be pleasing. A rotary broach or wobble broach could probably do hex socket and Torx but cross heads are forged I think so not a practical proposition for most people, the broaching is quite an ambitious method but it has been discussed on the forum and in the magazine. Of course the plain slotted screw is easy to make if they are appropriate for the job. Unless you have some sort of facility to do repetition work I think making more than a few of something will soon tax the will to live.


Thanks for your answer, Mike. I sensed this was the way things were, though I didn't know you could broach Torx slots.

Andy Carlson24/10/2020 22:29:37
311 forum posts
124 photos
Posted by William Ayerst on 24/10/2020 14:54:21:

What brand should I be looking for, for taps and dies? Dormer? Presto?

Oh lordy. Way to kick of a huge discussion on here

Some brands aren't what they were. No doubt others will chip in.

I went for opportunistically picking up job lots of decent used ones - LAL, Warrior, Herbert. I got a few duff ones but ended up with a set that covers most of my likely needs for not too much money.

BSF/BSW for me because they mostly get used for mucking about with old lathes and other such British made kit. I also have some metric stuff - metric all bought new, mostly Sherwood.

I'm off back to 2FS land now before I cause any more trouble. Welcome to the ME forum BTW.

Howard Lewis25/10/2020 10:51:19
3779 forum posts
3 photos

Purely an aside, but with a 8 tpi Leadscrew, there are many more thread pitches than multiples, or factors of 8 that can be cut.

A correct selection of changewheels will allow many variations.

From time to time you will run across some of the various "standard" threads, as well as "specials" used by certain manufacturers, for their own particular purposes. As instances:

The Myford ML7 Lathe uses a "non standard" thread to carry the chuck. A 1.125" x 12 tpi Whit form.

The predecessor ML1,2, 3 and 4 started by using a 7/8 x 9 tpi (Standard 7/8 BSW ), then moved to a 7/8 x 12 tpi on the Mandrel. (The Leadscrew was 8 tpi, but the Cross and Top Slide Leadscrews were 12 tpi )

10 tpi makes graduating the handwheels with divisions equating to 0.001" so much easier!

Some far eastern lathes use a 2.25" x 8 tpi Whit form thread for the chuck and Mandrel!

"Screwcutting in the Lathe" by Martin Cleeve (No.3 in the Workshop Practice Series ) and

"Gearing of Lathes for Screwcutting" by Brian Wood will show how a variety of pitches can be cut by the correct selection of changewheels.

The changewheels do as their name says, CHANGE the ratio between the Mandrel and the Leadscrew.

As proof, recently, a Lathe with a 3mm pitch Leadscrew was used to cut a 4 mm pitch thread. The same machine has been used to cut 1.5 mm pitch threads (for ER collet holders ).

With suitable selection of wheels, a mini lathe with a 1.5 mm pitch Leadscrew can advance a tool by as little as

0.06 mm for each revolution of the Chuck. (The changewheels, on mini lathes usually cover from 20T to 80T in 5 tooth increments. In this case, there are two 20T and two 80T wheels in the set.

As in many cases, extra gears can be bought, new or secondhand, to duplicate, or triplicate if you so wish.

BUT the gears must be of the same DP and pressure angle, as well as the required tooth count! A 14 DP gear will be coarser and larger than a 20 DP one with the same number of teeth.

A 127T wheel will allow Metric threads to cut with maximum accuracy, but a 63T wheel will produce threads with acceptable error in most cases, on an Lathe with an Imperial pitch Leadscrew.

For most "standard" threads smaller than 1/2" or 12 mm, I use taps and Dies.

If it needs to be said, BSW and BSW are a different thread form from UNC and UNF. In some cases the pitches coincide, but they are not properly interchangeable. Metric threads are the same form, (60 degrees ) as UNC/UNF but are not interchangeable because of differences in diameter and pitch.

Model Engineer threads (40 and 32 tpi ) are Whitworth form, as are British Standard Pipe and British Standard Brass. Cycle threads are 60 degree form although the same 26 tpi as BSB.

BSP and NTP forms differ in both form and pitch.

BA, mostly used on older electrical fittings, as well as by modellers use another different thread form, and are basically Metric in dimensions.


All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Latest Forum Posts
Support Our Partners
Eccentric July 5 2018
Eccentric Engineering
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest