Adjustable threading dies

I recently bought a nice Cyclomatic CTL 618EM lathe in France
With it came a box of tooling
Among them these adjustable threading dies
I have never seen these Is this a French only item
I think its nice to show them to you guys




Peter

Looks like an "Acorn die".

I had to google that but yes Acorn uses the same concept as the 4 dies at the top

Anybody has seen anything simular as the dies at the bottem
worked with these or the Acorn ones and how easy is it to adjust

Peter

Got some acorns in number size screw threads along with one of the first Hardinge second ops/ turret here. They work well enough and were more or less current tooling in catalogs even up to 20 years ago.

They are on the brittle side, I broke a segment on one of the small ones with minimal tightening while trying some cuts to see how far it would adjust out of curiosity. Was probably under the minimum (3A fit?), but not by much.

Of course on manual machines the Acorn holder should float & release(factory ones do) and then you still have to reverse the spindle. Nothing like a geometric self opening die head. I re-purposed one of the holders as a releasing tap driver with shop made collets, and mostly use one of the geometric heads for OD threads.

smt

Small bicycle spoke thread rolling heads are often done the same way.