The Da Vinci Notebooks at sacred-texts.com
The mint of Rome.It can also be made without a spring. But the screw above must always be joined to the part of the movable sheath: [Margin note: The mint of Rome.] 347
All coins which do not have the rim complete, are not to be accepted as good; and to secure the perfection of their rim it is requisite that, in the first place, all the coins should be a perfect circle; and to do this a coin must before all be made perfect in weight, and size, and thickness. Therefore have several plates of metal made of the same size and thickness, all drawn through the same gauge so as to come out in strips. And out of  these strips you will stamp the coins, quite round, as sieves are made for sorting chestnuts ; and these coins can then be stamped in the way indicated above; &c
 The hollow of the die must be uniformly wider than the lower, but imperceptibly .
This cuts the coins perfectly round and of the exact thickness, and weight; and saves the man who cuts and weighs, and the man who makes the coins round. Hence it passes only through the hands of the gauger and of the stamper, and the coins are very superior. 348
17:347 : See Pl. LXXVI. This passage is taken from a note book which can be proved to have been used in Rome.
18:348 : See Pl. LXXVI No. 2. The text of lines 31-35 stands parallel 1. 24-27.
Farther evidence of Leonardo's occupations and engagements at Rome under Pope Leo X. may be gathered from some rough copies of letters which will be found in this volume. Hitherto nothing has been known of his work in Rome beyond some doubtful, and perhaps mythical, statements in Vasari.