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There are often traces of sulfur in brass. The addition of manganese causes MnS to be formed. This reduces the risk of cracking.
The 2010 Manganese-brass are 26.5mm
for example
Older coins are different size
Yes. For example, US $1 coins minted since 2000 are struck in a brass alloy that includes copper, nickel, zinc, and manganese.
Steel
Brass
Solder
Pewter
No it's not. The outer layers of Manganese Brass give the coin the gold color.