Locks on plastic comb binding almost always start with the larger diameter sizes. They start with 1 1/4" through 2". The main reason for locking ends on the combs is for the stability of the book. The shear weight of the paper on the larger sizes tends to pull the fingers apart and pages can be lost. The locking ends prevents this from happening and protects the book. Some manufacturers offer three locks on the larger combs, but typically there are two locks on the larger combs.