the case indentify a pre war produktion becaus the 3 holes on the back.
It is a version as made after the war. Possibly old rectangulars were used and adapted.
In a 1970's leaflet-cataloque from Overhoff, page 14, such a buckle-type is noted as article-number 0779/45 mm Maurer. In the same series were available: Zimmerer (carpenter- 0778) and Dachdecker (roofer-0785).
From various visits to Overhoff I know they had crates loaded with messing rectangulars in the attic and storage capacity, for example versions with Imperial devices. I got tens and tens of them.
"Wir sollen auch unser Leben für die Brüder lassen" (1.Joh.3.16):
zum Gedächtnis Wilhelm Schenk. Er starb fürs Vaterland am 13. Juni 1916
As I have understood this buckle post-war. Buckle box probably defective made in war