Hello, this one was found in a Flak battery
on the back, there is a piece of alu(i think)
Nice buckle and hard to come by, shame about the condition though, here one for example and a previous thread on these buckles
Flat Back Luftwaffe
It is an interesting construction. I wouldn't call it rare. There are at least 5 member that have one. Here are four different styles of construction. The flat back is the hardest to find of this group. Ben posted a Luftwaffe with a very interesting catch. That one is rare.
Here is an SA flat back. It is brass with a steel plate. It may be from the same company that made your Luftwaffe.
Agree. Rather not rare, rather uncommon in contrast to the classical design. Such SA buckle see first. Thanks for showing.