Lee Loader

Hello everyone, I'm new here and really enjoying the knowledge and information everyone shares.
I've been reloading here in the UK for 40 years - using Lee (50%), Lyman (30%), RCBS (10%) and Hornady/Pacific (10%) gear and moulds.
When looking at used equipment on the BIG auction site, I still see the black plastic seating stem retainer on dies for sale. When did Lee switch to an aluminium part, does anyone know?
I have a set of Lee 223Rem dies I bought new in the 1990s with plastic. I know about the month/year codes used in the past twenty years or so, which I use to help age dies.
Thanks for your time.

Never seen such a thing ..... A picture maybe ?

Yes, it's the black knob/adjuster for the seating stem which used to be plastic. They've been aluminium for all of this millennium, certainly. The lettering used by Lee has also changed over time. When did they stop using serifs on the lettering? I think this change may also help date used dies. I know Lee changed the profile of the crimp in pistol dies in the 1980s from a roll crimp to a modified taper. All this us useful when checking out used reloading kit.