# Thread gauges



## jaywhoopee (16 Apr 2013)

I'm looking for some advice on which set(s) of thread gauges to buy.

I like to buy old tools (and dream of one day buying old machinery!) and get them back to a usable state, but occasionally I find missing or broken screws, nuts, bolts etc, which I need to replace.

As many of these tools will be 50+ years old I'd like to have a set of thread gauges (preferably that work both internally and externally) that should give me a sporting chance of finding (or making) a replacement screw or bolt.

Would just a Whitworth gauge like this and its metric equivalent be enough or am I likely to encounter any other threads in British and American made tools (e.g. planes, planes, spokeshaves etc)?

I know I probably could just re-tap the hole for a metric thread, but I'd rather not if I can help it.

Thanks in advance

John


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## jasonB (16 Apr 2013)

A 60 degree set would be useful for UNC & UNF thread pitches which you are likely to find on US tools.

You could probably get away with a lower quality than M&W, something like these

http://www.arceurotrade.co.uk/Catalogue ... -and-Wires

J


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## Spindle (16 Apr 2013)

Hi

I'd go for the type you've linked to - keep an eye out at boot sales and on the bay, you'll soon pick up Moore and Wright or Starrett sets for not much outlay.

Regards Mick


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## bugbear (16 Apr 2013)

jaywhoopee":2ubn9nux said:


> I'm looking for some advice on which set(s) of thread gauges to buy.
> 
> I like to buy old tools (and dream of one day buying old machinery!) and get them back to a usable state, but occasionally I find missing or broken screws, nuts, bolts etc, which I need to replace.
> 
> ...



Whitworth and metric thread gauge have fitted every tool thread I've ever tried to measure, and that's been several over the years.

I've also never seen a tool using BA thread.

But be aware than tools have a nasty habit of using non standard threads - i.e. non standard pairings of diameter and pitch.

BugBear


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## Cheshirechappie (16 Apr 2013)

To accurately pin down the thread of screw of unknown specification, you really need to know three things; the major diameter (outside diameter), the pitch, and the threadform (60 degree, 55 degree, 47.5 degree or a special). Ideally, that means a micrometer or vernier calliper, metric and imperial threadgauges, and something like a toolmaker's projector to check threadform. Clearly, the last is not available to most of us, so a certain amount of commonsense can go a long way, here. An oldish British machine will most likely have BSW or BSF threads, a more recent American one may use UNC or UNF, and a German one will probably use Metric threads.

Thread gauges can't really differentiate between 55 degree (Whitworth and BSF) threadform, and UNC/UNF/Metric 60 degree treadforms, so one imperial and one metric should be sufficient. The other essential piece of 'kit' is a reference work with the various screw standards set out - a Zeus book will cover most eventualities, but tracking down a secondhand copy of 'Machinery's Screw Thread Book' will cover almost anything 'standard' that most of us will ever encounter.

So to summarise - a micrometer or vernier to check outside diameter, a metric and an imperial thread gauge set to check pitch, and a set of charts such as in the Zeus book to pin down which standard you have. That should cover most eventualities.


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## bugbear (16 Apr 2013)

Cheshirechappie":2hmi1v0n said:


> Thread gauges can't really differentiate between 55 degree (Whitworth and BSF) threadform, and UNC/UNF/Metric 60 degree treadforms



Neither can the quality of thread cutting in most old tools. 

BugBear


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## Cheshirechappie (16 Apr 2013)

bugbear":2dn0hvnv said:


> Cheshirechappie":2dn0hvnv said:
> 
> 
> > Thread gauges can't really differentiate between 55 degree (Whitworth and BSF) threadform, and UNC/UNF/Metric 60 degree treadforms
> ...




True enough! Especially on smaller threads, such as those usually found on handtools. In practice, it rarely matters much in such applications, anyway. It does matter on more highly stressed components; some machine applications such as power saw and power planer spindles come to mind - don't compromise on fits in these cases.


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## Eric The Viking (16 Apr 2013)

I have a battered copy of the Presto Counsellor, from the 1980s, which is a much-cut-down version of Zeus tables.

It doesn't cover everything you'll want, I expect, but I was pleasantly surprised to find that it is on line here.

Enjoy.

E.


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## antarmike (17 Apr 2013)

Cheshirechappie":lpghqcfh said:


> Thread gauges can't really differentiate between 55 degree (Whitworth and BSF) threadform, and UNC/UNF/Metric 60 degree treadforms, so one imperial and one metric should be sufficient.


True but thread gauges are more to do with matching the pitch. Although Whitworth and Unified course have for some diameters the same pitch it is not true for say 1/2" Whit 1/"2 UNC . which are 12 TPI and 13 TPI respectively. If you buy a Whit thread gauge set it most likely that it won't have 13 TPI (neither BSW or BSW use 13 TPI on any diameter) but if you buy Unified it should have 12 TPI for 9/16 UNC but this matches both 1/2" and 9/16 BSW TPI.

I am not going to think about all the possible TPI in BSF BSW UNF and UNC but only buying one set Whit or Unified risks not having all the possible TPI's you may encounter.

Thread gauges tend to only have the TPI you would encounter at that thread angle. ie a 60 degree thread gauge tends to have only the TPI for UNF and UNC.


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## bugbear (18 Apr 2013)

antarmike":26g37ti6 said:


> Cheshirechappie":26g37ti6 said:
> 
> 
> > Thread gauges can't really differentiate between 55 degree (Whitworth and BSF) threadform, and UNC/UNF/Metric 60 degree treadforms, so one imperial and one metric should be sufficient.
> ...



True - but only in principle.

A quick glance at my usual reference chart shows that the 1/2" 13 vs 12 TPI is the *only* pitch difference I can find between UNC and BSW.

Further, even when you include UNF and BSF, the vast majority of pitches used in smaller coarser screws (UNC, BSW) are reused for larger, finder screws (UNF, BSF). (e.g. 1/4" UNC is 20 TPI, but 1/2" UNF is also 20 TPI).

The practical upshot is that a normal BSW thread gauge will serve all practical purposes w.r.t. UNC, UNF, BSW and BSF.

BugBear


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## jasonB (18 Apr 2013)

I would say a UNC/UNF gauge is useful in the smaller sizes as Whit won't cover 28 or 32 tpi which would be common on screws being 1/4" dia and near as dam it 3/16" , the smaller sizes are also not covered by whit but less likely to come up.

J


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## Cheshirechappie (18 Apr 2013)

I have two imperial thread gauge sets, one a cheap one stamped 'India', the other by CK of Germany. Both cover a range of pitches from 62 tpi to 4 tpi, including all those mentioned above, and the oddities used in British pipe threads. The only pitch it doesn't cover (that I have spotted so far) is the 11 1/2 tpi used in the American National Pipe Thread (NPT) for nominal sizes of pipe between 1" and 2". Since most pipe threads we are likely to meet are the BSP ones, I can live with this.

If you're looking for an imperial threadgauge, don't worry too much about exactly which pitches it covers. If it has a good range between tiny and huge, it'll cover all most of us are ever likely to meet.


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## bugbear (20 Apr 2013)

Cheshirechappie":1tmuhr7l said:


> I have two imperial thread gauge sets, one a cheap one stamped 'India', the other by CK of Germany. Both cover a range of pitches from 62 tpi to 4 tpi, including all those mentioned above, and the oddities used in British pipe threads. The only pitch it doesn't cover (that I have spotted so far) is the 11 1/2 tpi used in the American National Pipe Thread (NPT) for nominal sizes of pipe between 1" and 2". Since most pipe threads we are likely to meet are the BSP ones, I can live with this.
> 
> If you're looking for an imperial threadgauge, don't worry too much about exactly which pitches it covers. If it has a good range between tiny and huge, it'll cover all most of us are ever likely to meet.



I checked my thread gauge - a car boot Chesterman (pre the 1963 Rabone merger) No. 885/2

It's marked WHITWORTH and has:

4,4 1/2,5,6,7,8,9,10,11,12,13,14,16,18,19,20,22,24,25,26,28,30,32,40,48,60

which is more than just whitworth!

BugBear


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## soulboy (24 Apr 2013)

Hi John, did you get the kit talked about above, if you're interested I have some for sale.
chris


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## jaywhoopee (10 May 2013)

soulboy":15mfcann said:


> Hi John, did you get the kit talked about above, if you're interested I have some for sale.
> chris



Thanks again Chris.

It all arrived safely. Now to figure out how to use it! 

John


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