It is in part because of the sizes of the quarter, half dollar, and silver dollar. The dime, quarter, and half dollar are all rashional in size and denomination. The silver dollar coin is approximately also 2 times the size (and obviously denomination) of the half dollar, but a little bit off.
I don't know why they chose those coins... Perhaps they were the most circulating, high denomination coins... The nickel would obviously not fit into the equation, so maybe they wanted to make sure it was easily distinguishable from dime and quarter. If it was the same composition with Reese's edges and all, it would have a similar story as the SBA dollar.
I Don't know exactly why, by that's my theory on their reasoning.
I don't know why they chose those coins... Perhaps they were the most circulating, high denomination coins... The nickel would obviously not fit into the equation, so maybe they wanted to make sure it was easily distinguishable from dime and quarter. If it was the same composition with Reese's edges and all, it would have a similar story as the SBA dollar.
I Don't know exactly why, by that's my theory on their reasoning.




















