2 3/8" X 2 5/78" (58mm X 63mm)

No markings

Picture courtesy Earnest Griffin

2 1/4" X 2 1/2" (55mm X 61mm)

No markings

Picture courtesy Dan Wagner

2 3/8" X 2 5/8" (60mm X 64mm)

No markings

Picture courtesy Earnest Griffin

2 1/2" X 2 3/4" (61mm X 67mm)

No markings

Picture courtesy Earnest Griffin