Collet noses:
If they have the 'Pat Pend Made in USA' on them, they are machined steel: the 'good' ones.
The cast units never have those markings, and have the wings and body cast as all one piece. The steel units have the wings screwed in.
There are also nice repros on the market, made of steel as well. No Pat Pend on those.
The cast units are made of a material that does not have the tensile strength of steel, most likely Zamac or another zinc-based alloy. Over time, the tension put on the top opening when they are tightened down will cause the opening to crack and 'tulip'. Eventually they will spread so much that they will not tighten on the hex rod no matter how far they are forced down on the collet plate.
They were an attempt at improvement: the original noses sometimes would have the wings break off, and the wings were also a little small and could hurt the fingers. The cast units were a little easier to grip, and the wings would never break off. But they have the other problem instead: that's the law of unintended consequences at work... ;)