Help Identify a stepped collet

[Hoyt]

I have a stepped collet I cannot identify. It's in the middle, with a 3AT collet on the left and a 5C collet on the right. The back bearing diameter is .74" and the length is 2.50" The large ID of the step is 2".

 

[Superburban]

Here, you cannot beat this site for collet dimensions.

C (and similar) Collets

 

[Hoyt]

Here, you cannot beat this site for collet dimensions.

C (and similar) Collets

I don't see it in that table.

 

[Illinoyance]

I would guess 6K for South Bend 10K. If so, I would be interested.

 

[Hoyt]

I would guess 6K for South Bend 10K. If so, I would be interested.

It doesn't match up with the dimensions shown in the table at http://www.tools-n-gizmos.com/specs/C_Collet.html

 

[whitmore]

I have a stepped collet I cannot identify. ...
back bearing diameter is .74" and the length is 2.50" .

From the aged patina, it's not anything terribly modern. If that 0.74" could be 0.750, my old-edition
Machinery's Handbook suggests Rivett #4OS (with 0.670- 20 tpi thread), Becker #2AB (1/2-20 thread),
Ames (.745-24 thread) which would be longer, and Seneca #2S, also longer (over 3").