Help! I would like some help identifying what I believe is a WWII German 20x110RB round

I will attach one picture (The Headstamp) as unfortunately I’m a new user here any help would be appreciated, For information, the headstamp has “gyu” “17k” and “43”. It also has a German proof mark that I think says W A A 8 8 but I’m not for sure. I’d really like to know what the manufacturer “gyu” could be, I’ve been lead to believe that it is a Czechoslovakian manufacturer.

I’m replying for more pictures.


more of the fuze



final of the shell

Yes it is czech under german occupation.
gyu - Gebr. Michera, M.-Pruhonu, Stara-Tura