Yeah those should be the standard black plastic buttons that are 1 1/4".
However, I have a mil-spec pea coat with alternative 1" metal buttons. I originally bought this jacket because the measurements were perfect and I was going to change the buttons for the black plastic. However, then I realized the metal buttons were only 1" so the buttonholes wouldn't accommodate the larger black buttons. In the end, I came to quite like the metal buttons and now I don't think I'd change them even if there wasn't the issue with the buttonhole size. Don't know if this is reliable info, but I read somewhere on the internet the metal buttons were used from sometime in the 1970s until I think 1984.
Interesting about the metal buttons. I have a vintage coat from 1955, and it has the standard plastic buttons. Forum member, "Peacoat", would have the definitive answer about the metal buttons.