The cut indicates the uniform length of hair which will be left when you use the designated blade.
Usually, higher blade numbers indicate shorter length ie: A #4 blade leaves 3/8 inch of hair, and a #40 leaves only 1/100 of an inch. For lengths longer than 1/2", use a blade guard or comb.
Oster Cryotech Blades are freeze tempered. As the blades are frozen to 300 degrees below zero, the steel molecules become denser, which increases the steel's durability. To the grooming professional this means that not only do Oster blades start out sharp, they stay sharper longer.
For the really big jobs or to speed up heavy clip-downs, be sure to see the new Take Down Quick (TDQ) Blades