# Why 9 x 0.75mm threads for the section



## airborne_r6 (Sep 8, 2012)

I am wanting to get into making kitless pens and as I have been researching the techniques and tools needed to do so I have seen that the majority of people use a 9 x 0.75mm thread for their sections.  Why? Especially given that the only die I have been able to find in this size is on ebay and of suspect quality.  Will the much more readily available 9 x 1.0mm thread size work just as well?

Sorry if I just opened a huge can of worms.


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## skiprat (Sep 8, 2012)

No, the 9 x 1 won't work as a replacement. 

9 x 0.75 means the diameter is 9mm and the depth and distance between the threads is 0.75mm

This means that they are 25% different

Just as a matter of interest, what makes you think the one you have found is dodgy? 
These odd size taps and dies are normally only made by special order by fairly good companies such as Tapco in USA or Sherwood in the UK


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## airborne_r6 (Sep 8, 2012)

The one I have found is on Ebay out of Hong Kong.  It is $11 shipped from China, and when you look at the picture you can see that it includes a groove and a hole to make them look adjustable but the die is not actually split.

here is the link:
New 9mm 9 x 0.75 Metric Right Hand Die M9 x 0.75mm Pitch | eBay

and since I can never remember when it is OK to post an Ebay link on the various different forums I am on here is the item#: 170869063421

I did just find one on Amazon that looks better.
Metric Thread Round Die,High Speed Steel 9.0mm -.75 X 1" O.D.: Amazon.com: Home Improvement


Victor and MSC both carry it but are out of stock.


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## skiprat (Sep 8, 2012)

Yep, I had a looksee and found many dodgy ones on ebay too. I must admit I'm surprised

You might be lucky if you put a 'Wanted' note here as there are a few guys that have them here but are collecting dust. :wink:


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## biednick (Sep 8, 2012)

An m9x1 should be okay.
Edit: imshould clarify. A 9x1 will work in place off the 9x.75, assumeing both mating parts are 9x1.


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## skiprat (Sep 8, 2012)

biednick said:


> An m9x1 should be okay.


 
Cool, thanks!!:wink:


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## mredburn (Sep 8, 2012)

Have you checked classic nibs for the 9 x .75 $25.00 for the set
CLASSIC NIB - FEEDS


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## Texatdurango (Sep 8, 2012)

Wayne, To answer your question...... *It's ALL ABOUT WALL THICKNESS!
* 
Many members bought the 12mm multi-start tap and die sets in group buys over the past several years.  It's all about simple dimensions, when you have a lower pen body that needs to have threads cut on the outside of the barrel for the cap to thread onto as well as the inside for the section to screw into your MAIN concern is (or should be) the remaining wall thickness.

Myself, I did a lot of experimenting over the years and found that the 9mm x .75mm was the perfect thread for me.  It gives me a decent wall thickness as well as enough wall thickness at the bottom of the section where the converter or cartridge snaps in place.

A few use the 9mm x 1mm tap and die because they already have them or that they are easier to find but you will have a pretty thin body wall and that equates to pens breaking in half at the weakest point.... where the inner and outer threads are!  Can that thread be used...... Yes! Does it create a very weak point....Yes!

If you use different taps and dies for the body to cap threads, experiment with different section to body threads and see what works for you, it won't always work out to 9mm x .75 mm.

When I make a pen using the 14mm cap to body threads, I use 10mm x 1mm threads for the sections.

Hope this helps more than confuses


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## skiprat (Sep 8, 2012)

Thanks for that Mike. I honestly didn't know that Roy kept those and that's a pretty cool price, esp for a split die !!


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## mredburn (Sep 8, 2012)

I believe, but Roy will have to confrim it that they are made by tapco.


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## skiprat (Sep 8, 2012)

Ah....I thought the OP wanted to mix and match an existing 0.75mm internal and use a 1mm die for the corresponding external.


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## airborne_r6 (Sep 8, 2012)

mredburn said:


> Have you checked classic nibs for the 9 x .75 $25.00 for the set
> CLASSIC NIB - FEEDS



Don't know how I missed those, that is where I was planning on getting a tap for the feeds, thanks for pointing them out.



Texatdurango said:


> Wayne, To answer your question...... *It's ALL ABOUT WALL THICKNESS!
> *
> Many members bought the 12mm multi-start tap and die sets in group buys over the past several years.  It's all about simple dimensions, when you have a lower pen body that needs to have threads cut on the outside of the barrel for the cap to thread onto as well as the inside for the section to screw into your MAIN concern is (or should be) the remaining wall thickness.
> 
> ...



Well at first it confused me because the diameter of the thread is not changing, only the pitch, but I found a great article on wikipedia explaining how the pitch does affect the diameter. The important points are the mathematical relationships between Dmaj, Dmin and Dp.  The Dmaj is the diameter expressed in the thread size, in this case 9mm and the other two diameters are calculated from Dmaj and the Pitch. For a given Dmaj, as P goes up Dmin and hence wall thickness go down. 







Here is the page:
ISO metric screw thread - Wikipedia, the free encyclopedia

This also explains why people use a 12mm x.75 instead of a 12mm x 1.0 thread for their caps.

Thanks a lot for the help guys.


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## airborne_r6 (Sep 8, 2012)

skiprat said:


> Ah....I thought the OP wanted to mix and match an existing 0.75mm internal and use a 1mm die for the corresponding external.


 LOL nope.  I guess I should have been a little clearer in the OP but I meant changing the thread size on both parts.


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## skiprat (Sep 8, 2012)

airborne_r6 said:


> LOL nope. I guess I should have been a little clearer in the OP but I meant changing the thread size on both parts.


 
What is it they say about USA and UK??  'Two great nations divided by a common language' :biggrin:


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## Ed McDonnell (Sep 8, 2012)

I'm just starting with custom work myself and here's what I thought I understood. 

With a M9 x ? tap, the major diameter of the tapped hole is going to be 9mm, no matter what pitch you choose.

The hole you drill for the tap will = 9mm - pitch.

So for M9 x 0.75 you would drill an 8.3mm hole  and for a M9 x 1.00 you would drill an 8mm hole.  Since the max diameter is the same, wouldn't the M9 x 1.00 with the smaller hole leave a thicker wall?

Where did I go wrong?  

Edit:  Looks like Wayne posted an explanation while I was typing.  Time to study up.

Ed


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## schreiber (Sep 8, 2012)

All right, all right!  Ordered 'em at ClassicNib.
Y'all can quit torturing me now...  <sheesh> 

New toys!  :biggrin:

I'd like to add:  Thanks OP and all the rest for this informative thread.


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## Texatdurango (Sep 8, 2012)

schreiber said:


> All right, all right!  Ordered 'em at ClassicNib.
> Y'all can quit torturing me now...  <sheesh>
> 
> New toys!  :biggrin:
> ...


Nah......... this isn't the torture part, this is the easy part!  Wait 'till you start making different size pens and trying to remember which bit you used for which tap, how deep you drilled and tapped and what diameter tenon you cut for which die and on and on.....

*TIP: *WRITE down the drills and taps you use for each pen you make and DOUBLE check everything is working THEN type up a nice "Cheat sheet" to use a month later when you want to make another identical pen!  A scribble here and a scrible there will just confuse a month later and make you ask yourself... "what the hell did I use that 6.mm bit for, I didn't even need it this time?" 

Currently I make four different size pens with half a dozen variations of each...... keeping up with all the drill sizes, now THAT'S torture! :biggrin:


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## Ed McDonnell (Sep 8, 2012)

Ok, using the forumlas in the wikipedia article referenced by Wayne I came up with the following.

Using a M9x1 instead of a M9x0.75 will leave a thicker wall on the coupler between the male cap thread (whatever size is used) and the female M9 section thread.

using a M9x1 instead of a M9x0.75 will leave a thinner wall on the section between the male M9 section thread and the hole drilled for clearance for the converter / cartridge.

The calculated wall difference between the two pitches is about 0.003" (three thou).

Anybody else do the calcs and get a different answer?

Ed


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## skiprat (Sep 8, 2012)

Well I haven't done any calculations but I can't see how there would be any difference. 9mm is 9mm, it shouldn't make any difference if you use a 0.5, 0.75, 1.0 or even a 3mm pitch, the 9mm would always remain.

Ah, I see where you're coming from :wink: If you had to cut a male thread on a 9mm rod then the depth you cut into it would be less if you used a 0.5 instead of a 0.75 for instance. mmm Ok. That would then leave you more material to drill down the middle of the same rod.


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## Ed McDonnell (Sep 8, 2012)

Here's the way I think about it without the calculations.

For a M9 x .75 you drill a 8.3mm hole.

For a M9 x 1 you drill a 8mm hole.

The wall on the female side of the M9 x 1 will be thicker than the wall on the female side of the M9 x 0.75.  By a little less the 0.3mm / 2.

The threads on the male M9 will be deeper on the M9 x 1 than on the M9 x 0.75.  (Smaller hole drilled means less meat on the screw).

If you drill a hole in the male M9 screw, the wall left will be thinner with the M9 x 1 than with the M9 x .75.

Having typed that, I'm not sure it was any clearer than the calculations.  

Edit: Looks like you got it while I was typing.

Ed


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## schreiber (Sep 8, 2012)

Texatdurango said:


> *TIP: *WRITE down the drills and taps you use for each pen you make and DOUBLE check everything is working THEN type up a nice "Cheat sheet" to use a month later when you want to make another identical pen!


Thanks!  Good plan.


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## airborne_r6 (Sep 8, 2012)

skiprat said:


> Well I haven't done any calculations but I can't see how there would be any difference. 9mm is 9mm, it shouldn't make any difference if you use a 0.5, 0.75, 1.0 or even a 3mm pitch, the 9mm would always remain.



That's what I thought too, and why I started this thread, but from looking at the math of it there is a slight difference.  I think that it comes from the clearances necessary for the threads but the article is not clear on that. I can see mathematically where the difference is but can't quite wrap my head around what is actually going on.  Could have something to do with trying to learn seizure, sleep, sex mood and psychosis disorders along with their associated antiepileptic, antianxiety, antidepressive and antipsychotic drugs as well as basal ganglia and cerebellar anatomy for a test on Monday.

wow, two people answered before me.


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## Rich L (Sep 8, 2012)

airborne_r6 said:


> The Dmaj is the diameter expressed in the thread size, ...



To be picky, the major diameter (Dmaj) in your thread form is _not_ expressed in the "thread" size designation. It_ is _the major diameter for female threads. Look at (H/8)*2 as the difference. Measure any 1/4 inch bolt, for example, and the major diameter will not be 1/4 inch. It all has to do with thread tolerance. An M9 x .75 means that the "9" includes full V-thread height and that's not likely what you want in your male thread result. In fact, most good quality full profile dies will try to lop off that H/8 and if your tenon is oversized for that you're making the die work too hard. If you want to run a 9mm die over your tenon you really want (H/8)*2 less than that in diameter so you get a nice fitting thread that's not too tight. Accordingly, if you follow the diagram posted your minor diamter for female threads is (H/4)*2 (Dmin) greater than that V-thread would suggest. The simple designations for diameter and thread pitch are just that and they do not account for tolerance and class of fit and that's where you get major and minor diameters that make a real difference.

This is particularly applicable for metal - for plastic you can grind through just about anything.

Some esoterica for those that give a  ...  you know.

Cheers,
Rich


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## airborne_r6 (Sep 8, 2012)

Rich L said:


> airborne_r6 said:
> 
> 
> > The Dmaj is the diameter expressed in the thread size, ...
> ...



Excellent point, and in fact to clarify even further, the 9 in an M9 thread size is the nominal (or in name only) size meaning that it does not necessarily reference any specific dimension of the thread but is just used to classify that particular size of thread.


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## azamiryou (Sep 9, 2012)

Here's perhaps a simpler way to look at it: wider threads are deeper threads, and deeper threads require removing more material.

If you can start with more material (e.g., a thicker wall) to compensate, no problem. If you can't (e.g. male thread on a tube with the ID limited by what has to fit inside and OD limited by what it has to fit inside), then you'll end up with a weaker part.


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## Lenny (Sep 29, 2012)

airborne_r6 said:


> Could have something to do with trying to learn seizure, sleep, sex mood and psychosis disorders along with their associated antiepileptic, antianxiety, antidepressive and antipsychotic drugs as well as basal ganglia and cerebellar anatomy for a test on Monday.


 
This kitless stuff has me confused! .... and now there's going to be a test!!!


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## ironman123 (Sep 29, 2012)

I am with you Lenny.


Ray


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## joefyffe (Sep 30, 2012)

skiprat said:


> No, the 9 x 1 won't work as a replacement.
> 
> 9 x 0.75 means the diameter is 9mm and the depth and distance between the threads is 0.75mm
> 
> ...


 
"Dodgy"?     I checked the link, Skipper, and I have to admit it looks a bit dodgy to me too.   "Dodgy" Hmmmmmmm!!!  From the location, I am afraid our buddy might get Shang Haid if he orders that one.    Hmmmm, "Dodgy"


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## frank123 (Sep 30, 2012)

9 x .75 isn't a commonly stock item at a hardware store but isn't really uncommon either.

Try an industrial supply house or industrial fastener supply distributor in your town, they can probably order one for you if they don't keep  them in stock.  Should probably be cheaper to get it that way too.

As mentioned earlier, a 1mm pitch will leave a pretty thin wall and can cause you some problems in some materials, ordering a .75mm just heads off the frustration of a broken section in advance.


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