Found this the other day. Front suggests happily that it's a George III coin. Back says "Duits Gr 5..6" and is countermarked with a vase stamp.
Dia 19.5mm, thickness 3.6mm, weight about 8.5g
Plenty of VOC Duit pictures about but I can't locate anything even remotely like this with any amount of Google trawling.
Anyone have a clue?

Thanks
Identified - moved to Exonumia forum - Sap