What type of buckle is this?

[DownNDirty]

Found at an 18th century home site. It is made of some sort of alloy and was silver plated; it has a diameter of 1.5 inches/38mm. Is it a belt buckle? Sash buckle? Knee buckle? Or some other type? Never found a round one like this.

Thanks

 

[toasted]

My buckle book has a whole category of buckles similar to that called Annular buckles. They had many uses and it most likely dates to early 18th century but possibly earlier

 

[DownNDirty]

Thanks. A friend sent me a link to examples of annular buckles and I agree that this is one of those.