That is just a tad bit over 23 mm & its 6.22 g. Weight. Its a copper alloy...and if not what I expect it could be...it's definitely a blank for a world coin that fits the weight ,and size... My thoughts is that it is a blank for a US two cent pc. As its weight is spot on for the 2 cent 6.22 g. And if sent through a roll up mill to finish the edge I believe that it would fit on a two cent pc perfectly...and I can't find my caliber but its the same thickness as a 2 cent pc. Your thoughts? Now it may of been a blank that the mint used for mintage of a world coin. As the US does produce for other countries. See image next to a 1867 us 2 cent pc.