Richard, I am shopping for cushion cut & trillion mandrels right now,
so have a number of catalogues’ mandrel pages handily marked. The
mandrel I’ve seen that is nearest your desired millimeter range is in
Frei & Borel’s 2002 catalogue: p.120, item LL 143.048, Quadrillion
Bezel 5-15mm. The length is 10 &1/2 inches. The quadrillion shape in
the illustration is the rounded square that is also often called
square cushion cut. No connection to any supply company, just a
fellow mandrel hunter.
Since I am mentioning names, thanks to Rio Grande for their generous
donation of the casting machine to the Orchid raffle.
Anne M. Kelly