The diameter of this onza is just over 30 mm, making it by far the largest 1750 issue. Most 1750’s have a diameter of about 28 mm. In 1750 a new style of planchet preparation was being introduced at the Lima mint in anticipation of the machine-struck coinage to begin in 1751. Round thick gold planchets of about 23-24 mm were prepared. Under the pressures created by a mechanical press, these p ...