Most people think that they are pennys due to the size approx 30mm.
but that are in fact HALF PENNIES.they were stuck by Matthew Boulton
http://www.coins-of-the-uk.co.uk/sixd.html picture courtesy of spink
thought a dundonian would have known better lol
@goo5e1 depends on the condition but on E-BAY there's one for £6.50
from a BNTA member (British Numismatic Trade Association)