THREAD IDENTIFICATION

Hi

I hope someone here might be able to help me identify an unusual thread size I have come across on one of my full size projects

The item in question has, as best as I can measure 18tpi, and is just over 14mm dia.

A 9/16 x 18 UNF tap will enter the nut but is loose although a 9/16 x 18 die will not thread onto the bolt

The thread angle matches the whitworth form better than the metric

All the other threads on the engine are metric, mostly fine, I thought it was M14 x 1.5 but my thread gauge shows that to be wrong

The engine is a French design built in Wembley probably late teens early twenties. Were unusual or uncommon imperial sizes used in those days?

I want to make replacement nuts as the originals are rusted badly

Any help would be greatly appreciated

Dougie

Dougie

9/16" SAE seems likely

[Society of Automotive Engineers]

Commonly used on pipe/hose fittings.

MichaelG.

If 9/16 is loose 14mm will be looser.

Next size up from that is 15mm which isn't that rare. perhaps 15 x 1.5 ? with it being French.

The turn of the century metric standards were nothing like today. Also could the thread be stretched a bit making the gauge not read correctly.

Tracy listM15 x 1.5 £10 each

I was threading M15 x 1 yesterday for the KM nuts on the end of fork truck motors.

Edited By John Stevenson on 05/02/2014 17:25:47

9/16 CEI 20 which is the 20tpi Cycle Engineers Institute thread.

J

It was not unusual to "buy in" an engine from another, usually larger, manufacturer.

Morris used Hotchkiss engines, for instance.

In the late Thirties, the British Salmson was a bit of an All Spare Parts, using a Salmson engine, Morris gearbox, and Ford wheels, so threads could be a real mixture.

That sort of thing persisted even in the sixties, carrying over parts from earlier models.

The Leyland Leopard bus/coach chassis was to Unified standards, but the Leyland 0600 and 0680 engines fitted, and their gearboxes, and axles were to the previous BSF/BSW standards. Brake adjusters from the BSF/BSW standard Tiger Cubs were interchangeable, so onc avehicle was in fleet service, one side could be A.F, and BSF size hexagon on the other!

And when, in the late 60s, the Overhead Cam 500 Series engine to metric standards was fitted, some hardware could be to a third standard. It just depended on which "era" the part the part had been designed.

So don't be too surprised by what you find!

The engine is French, so metric threads could reasonably be expected.

To my mind, unlikely to be 9/16 SAE, which is an American standard. Did SAE standards even exist that long ago?

However, as already said, in the early days like the twenties, standards probably were not so rigorously followed, in the motor industry, so it is likely that it could be a bit of a special.

It is not a pipe thread is it?

The Austin designed 803cc A Series engine used in the A30 and the first OHV Morris Minors, during the 50s used 1/8 BSP ball ended screws, with a 7/16A/F locknut , as the adjusting thread on the Rocker levers, and this probably carried over onto the Mini.

1/4 BSP is Whit form, 0.518 (13.157mm) OD and is 19tpi, which might be a possibility.

The French STILL use BSP threads for plumbing fittings such as Taps (Faucets) , referring to them as "Half Gas" , or whatever, size fittings.

Howard

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History 

MichaelG.

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Edit: Here is the direct link to the page about SAE

Edited By Michael Gilligan on 07/02/2014 11:40:30

According to W.A.J. Chapman in "Workshop Technology" part one, the United Thread was standardised at the Ottawa conference of 1945, and the United Thread standard was published in 1949. The book says that there are two threads, coarse, and fine, but there is also an extra fine thread, UNEF. These threads are based on the American Sellers thread. Ian S C

I have come to the conclusion that the thread I was trying to identify must be some kind of special

The stud the nut fits on is 15mm dia, the threaded part is 14.8 mm and is definitely 18TPI

I have tried to cut new nuts on my lathe but I am having no success so I'm hoping someone with better ability than me can help

Can someone make me four nuts to the sizes above?, I can supply the blanks and would cover any costs

Thanks

Dougie

If I sent you a generic 15 x 1.5 nut would you try it ?

I know you said 18 tpi but often the differences between physical and practical applications are not that great.

PM me if interested.

Thanks John, PM sent

19/32 x 18 is a thread size on some beer kegs I have discovered but cannot locate a tap or die

Dougie

definitely 18TPI

Sounds like it may be a "convenience thread" whacked out on an 8tpi leadscrew unit

20 on the mandrel and 45 0n the leadscrew gives a decent useable thread for a project

edit

Probbly used a piece of "standard bar" for the period at the same time but I don't know about dat stuf at that time

Edited By Ady1 on 22/02/2014 11:46:16

20 on the mandrel and 45 0n the leadscrew gives a decent useable thread for a project

Thanks Ady, but I dont know what that means

Dougie

Threadcutting stuff, if a project needs a basic thread then the guy who did it may have run the job off himself on an 8TPI lathe

45/20= 2.25

2.25 x 8TPI = 18 TPI

Which would explain why it doesn't seem to fit any standards

(This is only a theory btw)

edit

The easiest route I have found in a weird situation is to cut a delrin nut, which takes mere moments compared to working with metal

Then once you have a delrin one which screws on and feels right cut a metal one

Edited By Ady1 on 22/02/2014 12:17:44

Hello Dougie,

It might be obvious and you don't say, but if your lathe has a Myford gearbox, then you can cut that thread directly just by selecting 18 tpi on the gearbox. If not then Ady 1 has shown you the alternative which will do just as well .

Regards

Brian

I have a Harrison M300 and could in theory cut the thread but I have broken every screwcutting tool I have and get nowhere and I am rapidly running out of hex bar

I was out in the workshop earlier and may have come up with a solution, if I turn the old nuts to a diameter then bore a new nut blank to suit and  silver solder both parts together

Dougie

Edited By Dougie Swan on 22/02/2014 14:55:13

Hello Dougie,

That might turn out to be the most pragmatic solution in the end. It has become an expensive exercise in frustration I'm sure.

Regards Brian

Dougie, What size hex and thickness, if I'm send a few up that *may* fit then might as well be some you can use.

Hi John

I want the nuts to look like the originals which are pre war thickness

So around 25mm hex and 12-13mm thick

Thanks

Dougie

At the time your bit of machinery was made, and being French design, it probably would have a contempory French metric thread, which could be quite different to modern metric threads, otherwise it would have most likely been Whitworth, or BSF. Ian S C