This is a big one: 11.5 inches across. It's in excellent shape considering it was copyrighted in 1969. Maybe this is an older printing.
I know a lot about sewing but next to nothing about knitting. This appears to be a wheel for a basic raglan sweater pattern you can make in just about any size you'd want. I love that there's a category of "sub teen".
You can see there is some color-coding happening here. If you are working on the front, you match the greenish-beige section of the inner disk to the same-colored section on the outer, according to the size you're making.
I don't know why we buy wheels like this, though. It's really no great shakes, unless you happen to be a fanatic about raglan sweaters.