Cutting Dies vs. Re-Threading Dies

[cg285]

i have 2 snapon sets that are 12point

 

[MrWhoopee]

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.

 

[projectnut]

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.

 

[ezduzit]

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

 

[Bob Korves]

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...

 

[Canus]

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%.