# What Size Rod To What Size Die



## Swerdk

I know this seems incredibly basic but I can't figure out the answer what is the proper size that you're Metal rod has to be for the die you want to use.
You might say well if you're using a 1/4x 20 die, your rod should be a quarter-inch. But what if you are trying to match 10 x 24 or 6 x 32. Maybe it would be helpful if I understood what the 10 stands for in the 10 x 24 I know that 24 is the pitch.   I do not mean to digress I just want to be able to make my own screws from the dies


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## RJSakowski

Here is a table that will tell you what you need to know. http://www.hobby-machinist.com/threads/cutting-threads-depth-of-cut.37700/#post-322311


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## Bob Korves

There are charts like this all over the internet and in publications like Machinery's Handbook.  None of this is a well kept secret.  The outside diameter of the thread is listed under major diameter.  In actual practice, most threads are made with a smaller major diameter than the nominal size.  To make a 1/4" bolt, you start with a rod at least .005" smaller than the nominal size, .250".  It depends on the percentage of thread you want.  Especially with dies, if you start with a .250" die you will soon be in trouble, too tight in the die...


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## Ulma Doctor

Hi Swerdk




maybe this thread chart may shed a little light.
for example,
a # 10 is .190" for the major outside diameter.
if you wanted to cut a screw in 10-32 tpi you'd start with rod larger than .200"
if you wanted to make a nut in 10- 32 you'd need to drill a hole .150" in diameter and then run a 10-32 tap in the hole


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## Bob Korves

There are also calculators online.  A typical bolt thread is cut at  somewhere around 65% of a full thread, which is much easier to cut, and is about 90% as strong.
http://tapcalculator.com/

Edit:  Here is a useful assortment of calculators:
http://www.amesweb.info/Screws/ScrewCalculators.aspx


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## Billh50

The size rod you will need is the major diameter of the thread you will be cutting with the die. Just find the thread on the chart and go by the major diameter.


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## CluelessNewB

So besides #5  (1/8" rod) nothing under  1/4" seems to be a standard off-the-shelf rod size.  How convenient .   And #5 isn't a very common size.


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## Bob Korves

CluelessNewB said:


> So besides #5  (1/8" rod) nothing under  1/4" seems to be a standard off-the-shelf rod size.  How convenient .   And #5 isn't a very common size.


None of us invented the system.  It is what it is, and we need to live with it and deal with it.  This is why we have machine tools and reference sources.  Rod can be ordered in number and letter sizes, I have an assortment of W-1 drill rod, numbers 1-60, 18" long, that I bought from Brownells about 30 years ago.  It is convenient for making all kinds of stuff.


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## ronzo

Multiply the number size by .013 then add .060.
Ex: #10 X .013 = .130 +.060 = .190
6 X .013 = .078 + .060 = .138
4 X .013 = .052 + .060 = .112


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## Swerdk

Thank you guys for explaining this I know it might seem basic but between work and raising a family the Learning percent leftover in my brain is about a half a percent-- I do better on the weekends when my brainpower raises to 1 1/2% 


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## T Bredehoft

No. 10, at .190 would work well with a 3/16 (.1875) rod.


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## CluelessNewB

Bob Korves said:


> This is why we have machine tools



That's what I keep telling my wife!   

Most times that I have needed to thread smaller sizes it has been something turned anyway like a shoulder bold or spacer with threaded ends so stock needed to be larger anyway.  The only exception that I can remember was a replacement electric motor thru bolt #8.  I ended up using all-thread.


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## Bob Korves

Fairly often I would like to put a thread on the end of a piece of stock, for instance a 1/2-13 thread on a 1/2" rod.  It would seem to be easy, just take a die and cut the thread.  But it is not usually that easy, because the rod is too big to cut a thread on it with a die, as it it a bit too large and can jam up and break something if you try to force it.  So the rod needs to be turned down a little to the correct size for an easy to thread size.  No problem on a 4" piece of stock, but I have needed to do it to an 8 foot piece of 1/4" stock, for instance.  I was able to get it done by properly supporting the rod along the entire length that stuck out of the left side of the spindle.  It was a good thing I placed the lathe with this in mind.  So, I do understand the OP's frustration.  We just need to deal with it the best we can.


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## P T Schram

Drill rod is another product I use to meet Enco minimums


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## Swerdk

Humor- i found the main problem.  I mistook harbor freight dies for dies that actually can cut carbon metal.   Bought a simple 6 dollar die and work accomplished. 


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## BROCKWOOD

Another issue with all this is getting the die not wander away from 'true'.  Countless times I've mounted the part to be threaded in the lathe & backed up my die holder with the tailstock & turning by hand... I still end up with a jake legged thread. Not square, true, parallel with the rod at all.  Once I get my BXA tool holders to fit my lathe:  I'm making die feeders (sorry can't think of their proper name). 

At this rate I will never be considered a Machinist; but I will have been a Tool Maker!

I hope this is not considered too inappropriate as I'll paraphrase:  You can climb poles your whole life & Never be called a Lineman; but suck just 1 (fill in the blank) & you're labeled for life.  Point is, we are All learning And sharing = we learn from each other.  But, yeah gotta reduce your overall dimension before threading.  Think of it this way:  The nominal size, like 1/4"  requires a bit of give from the bolt & also from the nut.  Charts given above by others should have you on your way! & a few YouTube videos should help me to have my new tool for cutting those threads straight as well!


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## mikey

Brockwood, you are referring to a Tailstock Die Holder - useful tool. 

This is an old thread but on the off chance that some new guy will see it, I'm attaching the best chart I've seen for sizing the rod before screw cutting or using a die. You need to determine the class of fit because this determines the rod size used before cutting the thread. Note that a class 2a is a looser fit than a 3a and the starting diameter ranges are tighter. The stock is turned to the OD limits for the class you need and this allows you to obtain the needed pitch diameter range you need for that fit. 

For example, for a class 2a, 1/4-20 external thread, you would turn the work to a diameter between 0.2489 to 0.2408. Then you put a 30 degree chamfer on the end and thread it or screw cut it. Then you check with three wires or a pitch micrometer to be sure your pitch diameter is between 0.2164 and 0.2127" and this should allow that work piece to fit any class 2b nut.


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## whitmore

CluelessNewB said:


> So besides #5  (1/8" rod) nothing under  1/4" seems to be a standard off-the-shelf rod size.  How convenient .   And #5 isn't a very common size.



OH, they're standard sizes, all right, but from the age of uncalibrated tooling.   #0 through  #12  are 
from a standard published 1907 by ASME.  Wire sizes were likewise
various; salesmen would have a book of samples, and you'd match diameters and 
order the 'gage' you needed.   Fit-and-try, not measure, was the common practice

#5 is not such an uncommon size, actually: it's 1/8 inch diameter.   I once needed to
thread some tubing 1/8"-40tpi lefthanded, and the die was available off-the-shelf.   But, it
came labeled "#5-40 LH".   

Granddad's old threading tools are adjustable; you'd keep tightening the
die plates against the thread and working it until it fit into your nut.    Any blacksmith
could harden the thread to make a new tap, or file a rod, for cast iron and wrought iron; the grinding
of HSS tooling came later.


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## BROCKWOOD

mikey said:


> Brockwood, you are referring to a Tailstock Die Holder - useful tool.
> 
> This is an old thread but on the off chance that some new guy will see it, I'm attaching the best chart I've seen for sizing the rod before screw cutting or using a die. You need to determine the class of fit because this determines the rod size used before cutting the thread. Note that a class 2a is a looser fit than a 3a and the starting diameter ranges are tighter. The stock is turned to the OD limits for the class you need and this allows you to obtain the needed pitch diameter range you need for that fit.
> 
> For example, for a class 2a, 1/4-20 external thread, you would turn the work to a diameter between 0.2489 to 0.2408. Then you put a 30 degree chamfer on the end and thread it or screw cut it. Then you check with three wires or a pitch micrometer to be sure your pitch diameter is between 0.2164 and 0.2127" and this should allow that work piece to fit any class 2b nut.



Nice chart Mikey!  Thanks for sharing!! Thank you:  Yes, tailstock die holder is the term I was suddenly at a loss for.

Whitmore filled in the blanks on the history of it all.  Thanks!  I do remember the reason electric wire actually uses a backwards gauge reference, as compared to metal, is because it was believed that wires would only get smaller way back then.  Now 4/0 copper (0000) is considered small for many applications.  Thank you all for sharing & maybe the Op will rejoin his thread & catch us all up on his progress.


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## schemer

mikey said:


> Brockwood, you are referring to a Tailstock Die Holder - useful tool.
> 
> This is an old thread but on the off chance that some new guy will see it, I'm attaching the best chart I've seen for sizing the rod before screw cutting or using a die. You need to determine the class of fit because this determines the rod size used before cutting the thread. Note that a class 2a is a looser fit than a 3a and the starting diameter ranges are tighter. The stock is turned to the OD limits for the class you need and this allows you to obtain the needed pitch diameter range you need for that fit.
> 
> For example, for a class 2a, 1/4-20 external thread, you would turn the work to a diameter between 0.2489 to 0.2408. Then you put a 30 degree chamfer on the end and thread it or screw cut it. Then you check with three wires or a pitch micrometer to be sure your pitch diameter is between 0.2164 and 0.2127" and this should allow that work piece to fit any class 2b nut.




Thanks for the chart Mikey. I have to cut some 2 1/4-8 threads and couldn't find the info I needed until I found this. I have an old machinery's handbook with a 1948 copyright date and couldn't find it in there either. It may be in there but the book is the small size version and its hard on the eyes. 
schemer


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## mikey

schemer said:


> Thanks for the chart Mikey. I have to cut some 2 1/4-8 threads and couldn't find the info I needed until I found this. I have an old machinery's handbook with a 1948 copyright date and couldn't find it in there either. It may be in there but the book is the small size version and its hard on the eyes.
> schemer



You're welcome, Schemer. That is the most complete chart I've seen - glad it helped you.


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## MarkM

Something to bare in mind.  With Mikey s example there is just about .008" difference on the nominal diameter and less than .004" tolerance on the pitch diameter.  Most charts are based on the single depth thread for straight plunging of .6134 times the pitch and threading with the compound at 30 degrees is  .750 times the pitch and if the nominal size is on the low end of the tolerance you may not get the class of fit your after.  Check your pitch diameter before your final cut.


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## rgehrig

Great links and charts


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