I've just bought a Garrett Ace 250 metal detector
Heavy bronze button

Old bronze buckle

I'm assuming this is a buckle but there's no apparent facility for a clasp so I cannot be 100% sure.

It is also old: how old, I don't know.

You can clearly see a simple pattern on the face side but it's plain on the reverse. It is also quite weighty for its size. If complete I'd say it would form a square with 2" (50mm) sides.

I found the buckle about 50 metres from the bronze button (although on different days)