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# Uncertain of Imperial based thread sizes

#### john.k

##### Diamond
Generally avoid 7th ,and so 14hts ..because they are infinitely repeating numbers........OTOH,some may consider 7ths lucky,and 14 ths twice as lucky.........or should that be 1/2 as lucky............aaaagh ,these damn fractions are doing my head in!

#### guythatbrews

##### Stainless
Why is a 10-32 thd is OK, but a 13/14-17 is not?
Well because #10 is a recognized size whereas 13/14 is not the usual way anyone does things. If you want a .9285 major diameter then say .9285-17, instead of hunting for a fraction that happens to fit. I guess you could call out a 24-24 thread and use the formula for figuring the major diameter of a numbered thread, but why would you?

BTW a 24-24 would be a .372-24 but lets call it a 59/159-24 instead. Pretty much works so it's ok.

If you don't stick with a standard you just create confusion. As the OP did when he said the 13/14 major diameter was .875. Can't be both, huh?

You can do anything you want to do. I'm glad everyone doesn't. What a confusing mess that would be.

#### William Lynn

##### Aluminum
You can do anything you want to do. I'm glad everyone doesn't. What a confusing mess that would be.
I've seen assemblies using uncommon dimensions for no reason except to try and force the consumer to buy parts specifically from their company, because some brain child thought it would be a good idea. In a couple of instances I was in on, we reversed engineered the part and made it in house and never bought from that company again.

#### SeymourDumore

##### Diamond
If you want a .9285 major diameter then say .9285-17, instead of hunting for a fraction that happens to fit.
Oh, I am not disagreeing with that at all, decimal is the way to go, but the fractional definition is just ... meh, who cares.

#### SeymourDumore

##### Diamond
I've seen assemblies using uncommon dimensions for no reason except to try and force the consumer to buy parts specifically from their company, because some brain child thought it would be a good idea. In a couple of instances I was in on, we reversed engineered the part and made it in house and never bought from that company again.
Soda Stream, would be a good example of that.
But then there are times though where special threads are pretty much required for fit, form or function.

#### dieselpilot

##### Aluminum
I am still not understanding the grief?
NS means it's a special thread. Period!
I may be wrong, but It's dimensions do not need to be called out explicitly ( though would certainly be nice ) if they can be calculated.
It is a non-standard thread size but it is of a standard thread form, therefore it can be calculated.
That is opposed to a standard thread size with non standard thread form, where each and every dimension needs to be specified.
For eaxmple a callout of .5000-20 UNJS must be followed by the list of dimensions that are not to the standard or description of the modification.

Contrary to what you may think, the above .928-17-NS is NOT a modified thread, it is just not standard.
And if they choose the 13/14 fraction instead of .928 decimal? Who gives a shit!
Why is a 10-32 thd is OK, but a 13/14-17 is not?

Are you reading the print or just guessing?

13/14-17-NS-3

Major DIA .875
Pitch DIA .8
Minor DIA .786

#### SeymourDumore

##### Diamond
Are you reading the print or just guessing?
Fair'nuff, I completely missed his writing of the diameters in the OP. My bad!

In my defense though, Y'all got hell bent out of shape about them 13/14 and UNS stuff that I got distracted.

#### kenton

##### Hot Rolled
If I see 13/14" called out on a print I will question it. It is a non standard fraction and makes me assume someone f'ed up the print.

If your customers would rather you make scrap than ask about a print more power to you.

#### michiganbuck

##### Diamond
An easily recognized thread can be found in reference material like a machinists handbook, or a thread chart/thread calculator .. a thing that seems odd is more chance of making an error.

#### dieselpilot

##### Aluminum
Fair'nuff, I completely missed his writing of the diameters in the OP. My bad!

In my defense though, Y'all got hell bent out of shape about them 13/14 and UNS stuff that I got distracted.
It doesn't say UNS. It says NS. There is no 17 pitch in the old American Special threads. It took exctly one web search to find the old standards, which haven't been in machinery's handbook for who knows how long. For that matter, 17 pitch isn't in the Unified standard either.

If you decided to make a 13/14-17 thread in your shop, go right ahead. If this is a "not my problem situation", that really doesn't help things along. It should be as obvious as stubbing your toe first step out of bed in the morning. 50 years ago if you had to sit down and calculate the diameters (disregarding the additional call outs) to produce this thread, you would have stopped and thought about it. Even if you did that, how many manual lathes(dating to the spec's era) have a 17 pitch thread feed? Today, you plug it in here or there, or ask online and someone with no skin in the game does it for you, and CNC makes whatever nonsense you program.

Anyway, I hope OP comes back with an answer from the customer as I am curious.

#### notreallyolivertwist

##### Plastic
It doesn't say UNS. It says NS. There is no 17 pitch in the old American Special threads. It took exctly one web search to find the old standards, which haven't been in machinery's handbook for who knows how long. For that matter, 17 pitch isn't in the Unified standard either.

If you decided to make a 13/14-17 thread in your shop, go right ahead. If this is a "not my problem situation", that really doesn't help things along. It should be as obvious as stubbing your toe first step out of bed in the morning. 50 years ago if you had to sit down and calculate the diameters (disregarding the additional call outs) to produce this thread, you would have stopped and thought about it. Even if you did that, how many manual lathes(dating to the spec's era) have a 17 pitch thread feed? Today, you plug it in here or there, or ask online and someone with no skin in the game does it for you, and CNC makes whatever nonsense you program.

Anyway, I hope OP comes back with an answer from the customer as I am curious.
Gosh, I did not expect this much feedback. It turns out it's a completely customized part for the individual, I have never seen this before. Hence why when attempting to research it myself, I yielded no results. Another reason I thought I would ask here as I managed to pull up the old standards and found nothing there, leaving me to wonder if it were some conversion issue or another. It is their own design and I honestly can't explain their logic behind it.

#### guythatbrews

##### Stainless
Gosh, I did not expect this much feedback. It turns out it's a completely customized part for the individual, I have never seen this before. Hence why when attempting to research it myself, I yielded no results. Another reason I thought I would ask here as I managed to pull up the old standards and found nothing there, leaving me to wonder if it were some conversion issue or another. It is their own design and I honestly can't explain their logic behind it.
It would have saved a lot of back and forth if you would have said this was a customized part for an individual up front. It seems maybe someone is planning to block competition by making a weird thread as several have said. It's a crazy notion I think but certainly not unheard of.

Going back to your first post, if you were provided 13/14-17 AND the major, minor, and PD, then the author of those numbers made a mistake and maybe you should confer with the author. They do not jibe. If you calculated those diameters toss them and use the numbers provide by the thread software several folks have posted.

About asking the customer most don't mind and if there is any doubt my policy is to ask. Long time ago, before google translate, we had a drawing that said M6x1 (insert Italian phrase here I don't remember what it was). Idiot boss said ignore it. We made around 100 M6x 1 Stainless Steel leadscrews and rulon nuts. All scrap the (italian phrase) specified a two start thread. A quick call to the customer would have saved loads.

#### Pete Deal

##### Stainless
Boy, I love that threadpal program. It paid for itself the first time I used it.

#### SeymourDumore

##### Diamond
It doesn't say UNS. It says NS. There is no 17 pitch in the old American Special threads.
17 pitch isn't in the Unified standard either.

If you decided to make a 13/14-17 thread in your shop, go right ahead. If this is a "not my problem situation", that really doesn't help things along..

My bad again, I did mean to write NS and not UNS.
With that though, a 17 pitch is certainly a perfectly valid candidate for the NS specification.
Even if you did that, how many manual lathes(dating to the spec's era) have a 17 pitch thread feed?

Who gives a Flying F about 50 years ago?
Back then if the customer really wanted a friggin' 17 pitch thread, you would have made a friggin' gear for your manual lathe.
Today, you plug in your numbers into the CNC program and hit Go! while thanking God for the technology that saves your ass from having to cater to special needs.

#### doug925

##### Titanium
Please tell me when it is proper to express fractions representing dimensions in the imperial system with a denominator of your choosing? Sure you can convert to decimal, but this stuff is standardized, not willy nilly.

You have a read a radically different story than I have. And that's the end of that story.
How about a 5/9th's & 7/9th's?
I did some work that was drafted by a French Engineer, working in the USA.
The above fractions were used on his prints. I was confused and had to ask for confirmation.
The owner of the Company told me I was not the first shop to call and ask about the crazy fractions this guy used.....

Either way, a fraction is just a messy way of calculating the decimal.... lol

#### michiganbuck

##### Diamond
qt Dieselpilot: (For that matter, 17 pitch isn't in the Unified standard either.)
And I don't think I have seen 17 on a lathe thread plate so it may be too special/odd to easily make
QT somebody (. It turns out it's a completely customized part for the individual, I have never seen this before.
>So it may be good for making a product with a single source for replacement parts.

#### guythatbrews

##### Stainless
qt Dieselpilot: (For that matter, 17 pitch isn't in the Unified standard either.)
And I don't think I have seen 17 on a lathe thread plate so it may be too special/odd to easily make
QT somebody (. It turns out it's a completely customized part for the individual, I have never seen this before.
>So it may be good for making a product with a single source for replacement parts.
But with CNC any pitch is game, and it shouldn't be too hard to figure this out. May have to fumble a bit but it can be done.

I wonder if the OEM is having gauges made? Or maybe they will shop make them. Gauges from a gauge company will be \$\$\$\$. Without gauges they may be in for future trouble.

A bit OT, but we used to make some parts with a 3/4 serrated spline, a job we got because nobody else had been able to make splines that would fit machines in the field. The old machines had obsolete ASME serrated splines, and the OEM engineer had made a new drawing with the current standard involute spline, which is close but doesn't interchange. It only took some measuring of an old male splines to figure out the problem. This was an end-of-life piece of equipment and no new female splines were ever going to be made, so it worked out. I think we made about 1000 of those parts. It was a good job. The OEM was told but they never changed the drawing!

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