OS20 is 22″. OS20 is 20″, but .
There are two wheel sizes under the 20″ category – the 20″ on Jr/mini bikes uses the 451mm diameter wheel in narrow widths (for 20-1/8″ & 20-3/8″ tires), and the conventional 20″ which uses the smaller 406mm diameter wheel but in wider widths. OS20 is 451mm wheel diameter in widths similar to 406mm wheels.
This fork will accommodate a OS 20” Wheel, as well as a 20 x 1 3/8″ wheel, but the fork is built for a Pro size rider and a OS 20″ Tire.
20’’ OS – 20mm front axle