Such cool patinas these clamshell charms have! The vintage metal might be brass or brass-plated, but we can't be sure, but we do know they are metal. Each shell is the same shape on both sides (hollow inside).
The little hanging loop is at the point of the shell. Each one measures 3/4 inch wide by almost 3/4 inch high (including the loop). The patinas vary as you can see by the two in the illustration, so please let us choose one for you.