1/2"-13NC | What the devil!?

[middle.road]

Got an oddball here I can't explain.
Markings on the shank:
HY-PRO
1/2"-13NC
HSS GS
HR7614-001
/- .1009 3112 (the first character is a 'slash' with a 'dash' in the center of it.)

This isn't your normal tap, it measures .599/.600"
I can't come up with an explanation for it.
Ah the joys of second-hand tooling.

The lower one is an actual 1/2"-13 tap.

 

[benmychree]

Perhaps it could be a Heli Coil tap.

 

[middle.road]

Perhaps it could be a Heli Coil tap.

That's what I was thinking, but the heli-coil taps that I have and have seen usually say 'Heli-Coil' on them.
But you're right, that's probably it. .050" / side sounds about right for a coil insert.
It is 13TPI....
I'm going to have to grind a mark on it or paint it red or something...

 

[benmychree]

My Heli Coil tap of that thread designation measures .604", perhaps yours is for a different (tighter) class of fit. Heli Coil taps are generally marked "STI", that is, stainless thread insert, the generic name of the trademarked insert.

 

[projectnut]

Most "heli Coil" (insert) taps carry the designation STI meaning "Screw Tap Insert. Almost all inserts use the same size threaded hole. Heli Coil is a brand name. Generally only those sold with the Heli Coil brand inserts have the name "Heli Coil" imprinted on them.

 

[middle.road]

My Heli Coil tap of that thread designation measures .604", perhaps yours is for a different (tighter) class of fit. Heli Coil taps are generally marked "STI", that is, stainless thread insert, the generic name of the trademarked insert.

Or perhaps it might be the desk side calipers I was using since I didn't brave the cold to run out to the shop for a mic.

 

[projectnut]

I took too long to edit my first post so here's the information in a new one.

Alcoa makes "Recoil" brand inserts that require the major diameter of the tapped hole to be .5999". It's possible the tap you have is for these inserts.

Here's a link to the Alcoa Recoil Catalog:
https://klsales.com/wp-content/uploads/2013/11/Alcoa_Recoil_Catalog.pdf

 

[middle.road]

I took too long to edit my first post so here's the information in a new one.

Alcoa makes "Recoil" brand inserts that require the major diameter of the tapped hole to be .5999". It's possible the tap you have is for these inserts.

Here's a link to the Alcoa Recoil Catalog:
https://klsales.com/wp-content/uploads/2013/11/Alcoa_Recoil_Catalog.pdf

AHA! The town right next to Maryville is named Alcoa. Hazard a guess as to why?
This tap came out of the goodies that I scored this summer where the gent had owned a local hardware store...
I didn't even know that Alcoa made inserts. I have never seen them in all these decades of tooling.

Now that Alcoa has renamed their manufacturing and processing Arconic I wonder what the town will do.
They changed the name on the plant's tower.
....