Thanks for your fast reply.
I actually discovered a stamp on the bottom of the propeller as you suspected (see picture below), whereupon you can find "hge" (probably the abbreviation for the propeller factory Gustav Schwarz in Eilenburg, Germany).
At the hub of the propeller I could find another lettering (see picture) on which one can only recognize the word "austauschbar" (="exchangeable" in english).
In addition to that the blade has a total length of 125 cm (=49,2 inch).
I hope this information will help.
Thanks in advance for your help.
Best regards,
John