2 1/8 is the size. It looks to be the table in your Avatar.
Brunswick Centennial, best table Bruns made later than the days of the Arcade.
FWIW - it isn't about the pockets, tho they do show this is an American
table. I've never seen a english/international table 5 x 10.
You want 2 1/8 balls to match the cushion height - your table has
triangular rubber, like a pool table, not the flat L-shaped used on English
Billiard tables.
American tables from 4 1/2 x 9 up to 6 x 12 use 2 1/8 balls. Note the
numbers on the 'colors'