Here's a neat vintage belt buckle from the mid to later 1940's or early 1950's. It is made of red plastic wrapped around a metal backing.  Even though the buckle is round, the design of the cut-out on the inside gives it an oval shape. 

The center bar is crimped in the center for possibly a fastener?  Or may have been used as a slide. 

Size is 2-3/4".