# Threads - Reverse Engineering



## EatenAppleCrafts (Jan 7, 2022)

Good morning, I am attempting to reverse engineer some threads for a customer, but I am a little confused.  The outside diameter on the barrel threads is ~11.5mm, and the inner diameter on the cap threads, to my best measurement, is ~11mm.  So, OD = 11.5, ID = 11.0, which would leave me to believe that I need a m11.5x.5 die, but I simply can't find one in existence.  Is my logic wrong, or am I just looking for a very rare die?

Thank you for any help,

Owen


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## PatrickR (Jan 7, 2022)

My first guess would be that they were cut on the lathe not with a die. are they single start?


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## Curly (Jan 7, 2022)

It is possible it is a proprietary thread or one of the obscure or little used ones. Victor Machinery carry a lot of oddball taps and dies in both metric and imperial. The measurements are close to 7/16 and could be one of those.


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## jalbert (Jan 7, 2022)

I would get a thread pitch gauge and measure them that way.


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## EatenAppleCrafts (Jan 7, 2022)

jalbert said:


> I would get a thread pitch gauge and measure them that way.


I did not really know those existed, though I guess I should have?  I just bought one online, and made sure to get the imperial as well just in case @Curly suspicion is correct.  Thanks all.


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## magpens (Jan 7, 2022)

EatenAppleCrafts said:


> Good morning, I am attempting to reverse engineer some threads for a customer, but I am a little confused.  The outside diameter on the barrel threads is ~11.5mm, and the inner diameter on the cap threads, to my best measurement, is ~11mm.  So, OD = 11.5, ID = 11.0, which would leave me to believe that I need a m11.5x.5 die, but I simply can't find one in existence.  Is my logic wrong, or am I just looking for a very rare die?
> 
> Thank you for any help,
> 
> Owen


@EatenAppleCrafts
Based on your reporting, I would say that the barrel thread ( meas. OD of 11.5 mm ) is probably a 12 mm.
Your meas OD is a bit on the small side for 12 mm, though . . . I would have expected the meas. to be around 11.7 mm.

Keep us updated, please. . . I am interested to know.

BTW, your suggestion of a M11.5 x .5 tap/die set puzzles me because you have not stated that your threads have a pitch of 0.5 mm
but that will be cleared up when you receive the pitch gauge that you've ordered.
You can, even now, get a pretty good idea of the thread pitch by using a metric ruler held up to the threads.
Many common pen threads have a pitches of 0.75 mm or 0.8 mm when the thread diameter is around 12 mm.


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## howsitwork (Jan 7, 2022)

magpens said:


> @EatenAppleCrafts
> Based on your reporting, I would say that the barrel thread ( meas. OD of 11.5 mm ) is probably a 12 mm.
> Your meas OD is a bit on the small side for 12 mm, though . . . I would have expected the meas. to be around 11.7 mm.
> 
> ...


I think he’s getting a bit confuse between thread pitch ( ie distance between threads) and thread depth (distance top to base of thread)  from the initial statement. As you say for pitch measure a number of threads then divide the distance measured by that number to get a decent approximation.

The pitch gauge should give a better idea .

If I am wrong in the above then I apologise


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## EatenAppleCrafts (Jan 7, 2022)

howsitwork said:


> I think he’s getting a bit confuse between thread pitch ( ie distance between threads) and thread depth (distance top to base of thread)  from the initial statement. As you say for pitch measure a number of threads then divide the distance measured by that number to get a decent approximation.
> 
> The pitch gauge should give a better idea .
> 
> If I am wrong in the above then I apologise


I though pitch and depth were the same for metric threads?  I see now a new rabbit hole, I've just been using taps/dies without truly understanding them.


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## jalbert (Jan 7, 2022)

You also have to consider that penmakers don’t have to adhere to thread standards. They can tweak them to their needs, so the pitch=thread depth formula is not necessarily accurate. For example, I use 1mm pitch threads for my caps (well, triple lead with a 3mm pitch, which comes out to 1mm between leads) but only cut my male threads to .75mm depth because I like a flatter crest.


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## duncsuss (Jan 7, 2022)

EatenAppleCrafts said:


> I though pitch and depth were the same for metric threads?  I see now a new rabbit hole, I've just been using taps/dies without truly understanding them.


Probably not, but it's a handy place to start when you are drilling a hole that's going to be tapped.

When I make external threads, such as the ones that a pen cap screws on to, I always make the major diameter less than the die is specified for. It avoids having sharp peaks on the threads, so there's the comfort factor, and there is also the fact that the "flat top" is much easier to polish than it would be if the peaks were a sharp point.

(John just posted the same thing, except he single-points the threads on the lathe, where I use taps and dies.)


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## EatenAppleCrafts (Jan 8, 2022)

Update... I received the thread gauge, and the threads are closest to 36g (Whitworth?), with the closest match being .7 in metric, but the 36g is closer.  So I am looking for a 19/64-36, maybe 7/16-36?


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## PatrickR (Jan 8, 2022)

EatenAppleCrafts said:


> Update... I received the thread gauge, and the threads are closest to 36g (Whitworth?), with the closest match being .7 in metric, but the 36g is closer.  So I am looking for a 19/64-36, maybe 7/16-36?


What are you  trying to do? Match to an existing cap?


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## EatenAppleCrafts (Jan 8, 2022)

PatrickR said:


> What are you  trying to do? Match to an existing cap?


I have both the cap and barrel, I am trying to create a new barrel, maker is unknown and the owner does not have the thread info for the pen (not that they should).  However, I am being asked to create a new barrel and section.  I can do it, but first just have to know the exterior barrel threads so that they can match the existing cap.


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## magpens (Jan 8, 2022)

@EatenAppleCrafts 
You ask ...... "So I am looking for a 19/64-36, maybe 7/16-36?"

Please check . . . . there is a big difference between 19/64 = 0.2969" and 7/16 = 0.4375"


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## PatrickR (Jan 8, 2022)

EatenAppleCrafts said:


> I have both the cap and barrel, I am trying to create a new barrel, maker is unknown and the owner does not have the thread info for the pen (not that they should).  However, I am being asked to create a new barrel and section.  I can do it, but first just have to know the exterior barrel threads so that they can match the existing cap.


that’s what I thought. Check the measurements on the cap, maybe the male threads have significant wear.
you could try bolts in the cap or take it to a hardware store to see what works.


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## magpens (Jan 8, 2022)

Reconsidering all the above, based on the preponderance of metric threads on pens,
I strongly think that what we are talking about is a basic thread size of 12 mm x 0.7 mm

Can you tell if the existing threads are "single lead", "double lead", or "triple lead" ?
That is a major consideration before obtaining a die.

It is possible the threads are not metric, in which case I would suggest  29/64 - 36 . . . but that seems odd sizing to me.

You measured, with your new gauge, and came up with a possible 36 threads per inch, which is extremely close to a metric pitch of 0.7 mm

A pitch of 0.7mm is pretty common on pens, as is a thread diameter ( O.D. ) of 12 mm . . . and likely triple or double lead


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## EatenAppleCrafts (Jan 9, 2022)

magpens said:


> @EatenAppleCrafts
> You ask ...... "So I am looking for a 19/64-36, maybe 7/16-36?"
> 
> Please check . . . . there is a big difference between 19/64 = 0.2969" and 7/16 = 0.4375"


That's a typo on my part, it is 29/64, much closer to 7/16"


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## EatenAppleCrafts (Jan 9, 2022)

magpens said:


> Reconsidering all the above, based on the preponderance of metric threads on pens,
> I strongly think that what we are talking about is a basic thread size of 12 mm x 0.7 mm
> 
> Can you tell if the existing threads are "single lead", "double lead", or "triple lead" ?
> ...


The weird part is that it looks like it is quadruple lead?, I tried my m12x.75 triple lead and it did not work.


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## magpens (Jan 9, 2022)

EatenAppleCrafts said:


> The weird part is that it looks like it is quadruple lead?, I tried my m12x.75 triple lead and it did not work.



Well . . . that puts a different light on  my suggestion. . . If a 12 x .75 did not work, then I am wrong.

I have never encountered a quadruple lead on a pen.


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## Curly (Jan 9, 2022)

magpens said:


> Well . . . that puts a different light on  my suggestion. . . If a 12 x .75 did not work, then I am wrong.
> 
> I have never encountered a quadruple lead on a pen.


The Baron and Sedona kit pens used to be a quad thread. I don't know if they still are but suspect they haven't changed.


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## magpens (Jan 9, 2022)

Curly said:


> The Baron and Sedona kit pens used to be a quad thread. I don't know if they still are but suspect they haven't changed.


@Curly
Thanks for that info, Pete. . . I have never made ( or even examined) either the Baron or Sedona.


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## magpens (Jan 9, 2022)

Curly said:


> The Baron and Sedona kit pens used to be a quad thread. I don't know if they still are but suspect they haven't changed.


@Curly

And, I believe, the Baron is a 10 mm Cap-to-Body thread. . . Correct me if I am wrong . . . anybody !  ( don't know the pitch )

Is the Sedona basically the same size pen as a Baron ?


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## Curly (Jan 9, 2022)

magpens said:


> @Curly
> 
> And, I believe, the Baron is a 10 mm Cap-to-Body thread. . . Correct me if I am wrong . . . anybody !  ( don't know the pitch )
> 
> Is the Sedona basically the same size pen as a Baron ?


It is the round ended version of the same pen. Much like the El Grande and Churchill are a flat and rounded ended.


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