The #'s are for different strength of lenses. Depending how bad your eyes are. They go in the Hooded peep made by Specialty Archery. But I think they might fit in the super ballpeep also.

At the shop I was at they had a rotating wheel with all of the different lenses in it. You held it in one hand and a handle with a fiber optic pin in the other looking thru the lens, and rotate the wheeluntill you have the sharpest picture.

Kinda like at the doctor. Is this better or this one.