I've never handled one of these, but that edge looks as though the coin could have been struck on a
planchet cast in a two-sided mould; they do have an odd appearance. A mould for these was found in Jerusalem; it consists of two
stone slabs, with one
face ground flat. Shallow holes were drilled, and linked together, so that the two slabs could be fastened together, and metal poured in. The hollows on each
side never matched precisely, hence the odd stepped appearance of the
flan.