Thanks for all your posts, its a relief to get the thumbs up. I did spend a couple of hours look through a couple of buckle data bases before making my post, came across the same moulded piece a number of times always with a slightly different post sleeve & prongs setup to mine, never did find a 100% match. Great for it to get a vote of confidence. I've included three pictures of the belt for everyone to see. Again thanks for the posts they've been a big help.
I would have said SA to be honest
A good representative buckle and in my opinion, no problems whatsoever.
Attached is an image of a similarly manufactured buckle, however by Overhoff und Cie. As can be seen, there are traces of the original silver finish. Interesting to note that the reverse "tool details" are exactly the same, even down to the style, positioning and boxing of the RZM logo and the M4/.
The strap shown is I think pre war "political" and could easily have been SA.
There is however a very crude "rule of thumb" when it comes down to establishing originally matching belts and buckles. Assess the buckle as "hard or soft", i.e., nickle silver or steel (hard) against aluminium or zinc (soft). A "soft" buckle in theory would never be worn with a leather strap which had a "hard" catch.
The reason is obvious, however as the war progressed, rules of wear were totally ignored and necessity and availability prevailed.