I know that the steel return rollers were introduced in the production line from october 1943 but as you see in the pic there are different styles.
Please could somebody clarifying me which correspond to which firm Krupp, Vomag or Nibelungenwerk
and when were put in production?
Many thanks.

Unless someone has already attempted a "counting heads" exercise to give general guidelines, I think you're stuck matching pictures with roller types.

For identifying features among Sherman tanks, legions of dedicated modelers/fans have pored over photos and survivors and tech manuals to compile various differences. I'm not familiar with a similar one for Pz IVs -- however, it'd be cool if one existed.

A while back, I tried to determine features based on factory and time of issuance of StuG IIIs. I used a combination of Spielberger, Panzer Tracts and the Achtung Panzer books and got some useful info. Maybe you can do the same?

Actually, Craig Ellis (8wheels-good) has been doing exactly that. If you go to Blurb, you will find his current collection of 11 books devoted to the Panzer IV series, and in many of the books he has done extensive work using various features to identify who built the particular vehicle as there are features specific to not only time frames but also manufacturers (Krupp, Vomag, Nibelnungen). His last book published is in fact the "Factory Production Guide" for the Ausf.G.

As for the Stug III, the History Facts books are probably the best reference for dates and production features, with well laid out charts and tables identifying features/dates/manufacturers.

As for the return rollers, I'll have to check and see if there is any correlation between type/date/manufacturer when I'm at home.

Many thanks to all. By the way I bought one of Craig Ellis book but it not arriving yet. I´ve been thinking to buy another three books in Blurb.
Recently I get Panzer tracts Nº 4-3 Pz IV H.J but although it is a very good book, it not discriminate between different steel rollers excepting in the text that names return rollers with roller bearings and plain bearings but there isn´t any sketch.

I bought the Craig Ellis books but even with them there is no clue yet about the different return rollers.