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# Uncertain of Imperial based thread sizes

#### notreallyolivertwist

##### Plastic
Hi everyone,

I was hoping someone could help me read how to construct the following thread:

13/14-17-NS-3

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

I understand the DIA bits but not the NS thread label.
Apologies if this is the wrong place to post this, however I am just struggling to find solutions to this.

Thanks

#### gustafson

##### Diamond
National Special
not a standard pitch

#### gustafson

##### Diamond
should be 7/8 by the dim, not uhh, 13/14

#### guythatbrews

##### Stainless
Several things look wrong there. Might be a total mistake on the part of the draftsman.

#### notreallyolivertwist

##### Plastic
Okay, it is a customised thread though that's manually done, I am not sure if that is a factor. However how would I know what the angle of the pitch is from this? I am not sure about the conversions from imperial to metric...

#### Mtndew

##### Diamond
Hi everyone,

I was hoping someone could help me read how to construct the following thread:

13/14-17-NS-3

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

I understand the DIA bits but not the NS thread label.
Apologies if this is the wrong place to post this, however I am just struggling to find solutions to this.

Thanks

Let's say that the O.D. is .875
And let's say that the pitch is 17 (definitely a special)
The listed minor diameter of .786 would be way too small for that pitch and should be about .820 diameter approximately.

#### guythatbrews

##### Stainless
Let's say that the O.D. is .875
And let's say that the pitch is 17 (definitely a special)
The listed minor diameter of .786 would be way too small for that pitch and should be about .820 diameter approximately.
The pitch diameter should also be more nearly in the middle of the major and minor.

13/14 = .929 and nobody ever uses fourteenths.

Something is rotten.

#### doug925

##### Titanium

Thread data for a 7/8-17 NPS

#### doug925

##### Titanium

13/14-17 NPS thread data

#### notreallyolivertwist

##### Plastic
Let's say that the O.D. is .875
And let's say that the pitch is 17 (definitely a special)
The listed minor diameter of .786 would be way too small for that pitch and should be about .820 diameter approximately.
Well, let me give it a bash with your measurements instead then. I do understand what you are saying. I just don't know how to read Imperial yet. First time I have used it. Do you know what the angle would be between each individual thread rotation for this? It does not give one and I am not sure how to figure it out

#### notreallyolivertwist

##### Plastic
View attachment 391701

13/14-17 NPS thread data

I see it's a paid software. I have one more that I need, would you be willing to write it up for me? I would really appreciate it:

15/16-16NS-1

Major DIA : .9375-.009
Pitch DIA: 0.8969-.0036
Minor DIA: 0.8608 MAX

Thanks again, I really appreciate the assistance

#### Mtndew

##### Diamond
I just don't know how to read Imperial yet. First time I have used it.

I was going off of a 5/16-18 thread where the minor is .257 diameter and the major is .3125 diameter.
So, if that difference is .055", then the 17 pitch would be close to that.
Your numbers have it at .089" which would be quite deep for a standard 60 deg thread.

Think of an M10 x 1.5 thread and the difference between the major and minor diameters.
The 1.5 pitch is very close to an imperial 17 pitch.
1.5 = .05905"
17tpi = .05882"

#### Mtndew

##### Diamond
Do you know what the angle would be between each individual thread rotation for this?
The helix angle? I don't understand why you would need this for a pitch this fine.

#### notreallyolivertwist

##### Plastic
The helix angle? I don't understand why you would need this for a pitch this fine.
I had been reading a bunch of thread documents online regarding imperial conversions and they were all referring to having angles. Hence why I was so confused. You are actually clearing a lot of the confusion up for me.

#### Mtndew

##### Diamond
I had been reading a bunch of thread documents online regarding imperial conversions and they were all referring to having angles. Hence why I was so confused. You are actually clearing a lot of the confusion up for me.
Some have different angles, but then you're getting into different styles of threads like Acme, Buttress, Square, etc.
All standard imperial threads are 60 deg included. The same as Metric threads.

#### notreallyolivertwist

##### Plastic
Some have different angles, but then you're getting into different styles of threads like Acme, Buttress, Square, etc.
All standard imperial threads are 60 deg included. The same as Metric threads.
Appreciate the clarity bro

#### notreallyolivertwist

##### Plastic
@Mtndew One last thing if you don't mind. What does the last number refer too? NS-3 for example?

#### michiganbuck

##### Diamond
I think it would be a good class assignment to design a special thread so to understand the mechanics of a screw thread..but to make something with an odd /special thread likely would be an engineering mistake.
60 deg included is best for some special thread.

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