Nice find Markus, it is amazing how square the catch is, I wonder if there are anymore buckles with a catch like that?
A nice HJ, Markus These injection-molded aluminum HJ's are scarcer than the die-stamped variety and if memory serves were only produced by Schröder and Sieper. If he sees this, Chad might have to correct me here but I think Schröder is the more commonly encountered maker with these. Interesting though that the most commonly encountered die-stamped aluminum HJ is the RZM M4/38 by Sieper. Attached is my example courtesy of a great deal from Chad
a very nice exemplar what you hold in your collection !