From the vintage 1930's or 1940's, a brown heavy plastic dress buck slide.  A nice stylish shape suitable for your sewing or craft needs.  Shiny surface which does show normal scuffing, as would be expected.  Otherwise a nice buckle.

Measurement:  3"  long, through the widest point.  2-1/4"wide, through the widest point.  Thickness:  1/8"