Here is the largest US coin ever made. It's the Buffalo Nickel. This one is over 3 1/2 inches across. Naturally it's Type or Variety 2, dated 1913-S. I wonder why? Lol and yes, it's a novelty. I believe they were designed as a coaster set but I'm not sure.
Is the 1877 pattern the same size as the 1915 Panama half union? I'd have to imagine so.. Edit - nope, I take that back. 1877 and 1915 half unions are different sizes. 1877 is 50.8mm and the 1915 is only 44mm. So you're 100% correct https://en.numista.com/catalogue/pieces124032.html https://en.numista.com/catalogue/pieces24934.html
Yup it is a coaster. bottom photo are mine... not sure where I put thee others... ??? The cent is my favorite.