Threaded endmills ?

[Jim F]

These came in a box of end mills from an estate sale.
Anyone ever see these?
I can make out "Clarkson", 1/4 and England on the shanks.

 

[JimDawson]

I have seen those before, 1930's vintage maybe? Nobody has used those for years.

 

[Martin W]

Threaded end mill are used on Clarkson type holders. The threads on these end mills look odd.

 

[benmychree]

The idea being that since they were threaded into the holder besides being firmly clamped, they would not creep out of the holder under cutting forces, as will smooth shank mills in collets sometimes will.

 

[brino]

I have seen them, and may even have a few.
I always wondered about them, glad you asked......
-brino

 

[bollie7]

You can still buy Clarkson collet chucks and threaded cutters new.
Can't see if there is a thread in the collets shown with the chuck, but they look the same externally as the threaded type.
With the asking price I don't imagine many hobbyists would be buying a new Clarkson chuck though.
Peter