Here is a buckle featuring a roundel which was undoubtedly made by the same firm which made those for the R. Thiel buckles:
Source: RBNr Militaria » OBJECT
Notice the different type of catch and also the lack of markings. It looks like the finish has worn away from this one, and it may have been ground dug.
When I initially saw this, I thought it was a fake, but then I noticed that the roundel is identical to those marked for R. Thiel.