Shun Zhi Tong Bao
rarest 1 cash coin

Metal: brass
Diameter: 23.7 mm
Weight: 2.1 g (0.6 mace; 1 mace = 3.781 g)

Werner Burger, 'Ch'ing Cash until 1735', 1976, Taipei, Taiwan:

       Peking fell into the power of the Manchu on 6^th June 1644, and with it all its nearly undamaged installations and institutions. All sources agree that in the first year cash were cast in Peking with the weight of 1 mace. The cash of the first two years can be arranged according to the same system used in the last years of Ch'ung-chen . The Manchu took over from the Ming dynasty three mints: an "Old" and a "New" Mint of the Board of Revenue and the one of the Board of Works. Initially the new Manchu rulers did not only take over all the distinguishing marks for the three mints (t'ung with one dot for the Old Mint of the Board of Revenue; for the New Mint, in addition, on the reverse the character hsin , new; and t'ung with two dots for the mint of the Board of Works). They also adopted the style of writing and the weight regulations.
       The weight of the Ch'ung-chen cash of the last years was in North-China officially 1 mace (in the South only 0.8). In reality, few of those late cash were heavier than 0.6 mace <see coin below - VB>, but the new Shun-chih cash are exactly 1.0 mace. Judjing from its great rarity the distinguishing character hsin for the New Mint have soon been abandoned, and their appearance must have been considered sufficient to distinguish them from coins from the Old Mint (smaller diameter, broader k'ou of chih , etc.).

Metal: brass
Diameter: 24.1 mm
Weight: 2.62 g (0.69 mace; 1 mace = 3.781 g)