# Cutting Dies vs. Re-Threading Dies



## Janderso (Apr 25, 2018)

I learned something today.
I was watching a Youtube, "Abom79" was describing the difference between the round cutting dies and the hexagon re-threading or chasing dies.
I have never heard that. My ATD jippo Tap and Die set only has hexagon dies.
I went online to Mcmaster Carr and validated this subject. It seems all those years I thought it was just a manufacturing preference.
OK, who is going to tell me I'm full of it? Go ahead.
I decided to replace my Imperial dies anyway so I am ordering 2-3 a month of quality McMaster Carr round cutting dies. That way of buying takes a bit of the pain away.
1" diameter dies $15 each
1 1/2 diameter dies $20 each
I purchased one each of the holders.
New day new lesson


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## benmychree (Apr 25, 2018)

Life is like that -----  When I was a kid, round dies at the local hardware store (Ace brand) were 50 cents each.


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## David S (Apr 25, 2018)

I saw the same video.  However I do have hex dies that have start side on one side and are intended for cutting not chasing.  They are carbon steel, not HSS.  I wonder if that makes a difference.   At our local hardware store there are many different sizes of thread cutting dies in Hex format..all "high carbon steel".

David


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## Janderso (Apr 25, 2018)

I did see in the Traver's tool site they do list threading dies that are hex, they are also carbon only. I guess as a rule of thumb, if they are round they are for cutting threads, if they are hexagon they may be cutting if carbon or chasing/rethreading if HSS.


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## Dave Paine (Apr 25, 2018)

I also learned about cutting vs re-threading dies a few years ago.   I do not think is it so simple that all round dies are for cutting and all hex dies are for re-threading.    My first tap and die set had round dies, and they did not cut new threads well.

My present set of tap and dies is hex dies.    These cut well in aluminium, but not easily in steel.  These are high carbon steel - I think.


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## brino (Apr 25, 2018)

Dave Paine said:


> I also learned about cutting vs re-threading dies a few years ago. I do not think is it so simple that all round dies are for cutting and all hex dies are for re-threading. My first tap and die set had round dies, and they did not cut new threads well.
> 
> My present set of tap and dies is hex dies. These cut well in aluminium, but not easily in steel. These are high carbon steel - I think.



I agree, it's not as simple as round vs. hex.
There's a lot to the manufacturer name as well.
Was your first set from the budget category?.......I once bought a set and when I threaded a die onto a bolt it was noticeably at a bad angle. That set was promptly returned to the store, and I started buying quality ones as singles.

-brino


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## Dave Paine (Apr 25, 2018)

I do not know the manufacturer of my old tap and die set.   It was sold under the Craftsman brand, may have been late 80's or early 90's.  This was likely a budget price range.  I did not appreciate the difference of budget vs quality for these tools at the time.


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## jdedmon91 (Apr 25, 2018)

Dave Paine said:


> I do not know the manufacturer of my old tap and die set. It was sold under the Craftsman brand, may have been late 80's or early 90's. This was likely a budget price range. I did not appreciate the difference of budget vs quality for these tools at the time.



I have the same set. Used them for years. In fact used the metric set to thread stainless for my longer tailstock lock handle on the Grizzly 


Sent from my iPhone using Tapatalk


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## Eddyde (Apr 26, 2018)

I still have the Ace Hanson tap & die set I got for my 18th Birthday. All but one of the dies are original, several have never been used. most of the common size taps have been replaced several times. My advice is, only buy what need, especially since they are only a day away from McMaster.


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## KBeitz (Apr 27, 2018)

I have one of those old green plastic case Ace Hanson tap & die sets. It has been a good set...


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## cg285 (Apr 27, 2018)

i have 2 snapon sets that are 12point


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## MrWhoopee (Apr 28, 2018)

Re-threading dies are almost always carbon steel. Cheap tap and die sets are the same. Calling them "re-threading" is a more honest representation, probably intended to control expectations and reduce complaints when they are used to cut new threads. You may be able to cut a few new threads with them, but they definitely will not hold up to tough materials or production use.

I recently bought an old, carbon steel, metric tap & die set off CL for $15. I knew what it was when I bought it, figuring it would allow me to chase some damaged threads, maybe tap a hole or two. If I need better, I'll buy the ones I need. When it comes to SAE (inch, imperial, whatever), I buy only HSS. I've been buying assorted lots of taps and dies off eBay and have built up a pretty complete set for not much money. Just got a 3/4 pipe tap, left hand no less. Maybe I'll relist that one.


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## projectnut (Apr 28, 2018)

I agree that it's not as simple as hex vs round.  I have a set of Snap On HSS hex dies purchased in the 1970's they were then and they still are today thread cutting dies.  Snap On still makes a version of this die set today.  The dies are now made so they can be used either in a standard die handle or in a socket or box end wrench.  In more recent times I have bought several HSS thread repair dies that are round.  They were a bit harder to find, but I wanted to use them in a tail stock die holder designed and manufactured for round dies. 

I think there is a preference for the rethreading dies to be  made in the hex form for a few reasons.  Often times a standard die handle won't fit into  an area where a thread repair needs to be made.  It would be difficult and time consuming to disassemble the component far enough to gain access for a die handle, or remove it completely.  The hex dies are made to sizes that will fit sockets, and open or box end wrenches.


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## ezduzit (Apr 29, 2018)

Generally, round dies are thread cutting and hex dies are re-threading.


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## Bob Korves (Apr 29, 2018)

The difference between a threading die and a re-threading die is in the geometry of the cutting edges, not in the external shape of the die.  With threading dies you want them to cut the metal, so a positive rake at the cutting edges is required.  For re-threading dies, you do not want to cut metal, but rather to push the metal back where it belongs.  For that a negative or neutral rake at the cutting edge is required.  When I am choosing a tap or die for a job, the first thing I look at (after checking for the correct size and pitch) is the geometry of the cutting edges, then how sharp it is...


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## Canus (May 3, 2018)

Also a re-threading die should NOT cut the root out of the thread.  As most bolts and studs are roll formed they have a rounded root to thr thread.  If a standard threading die is used on them the die will cut the root to a vee shape.  This can create a stress raiser thus reducing the strength of the bolt/stud by about 30%.


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