For a glossary of brush terms use this link..

THOSE CONFUSING BRUSH SIZES

(Are they the art world's tower of Babel?

A short answer is "yes." We're cursed with French sizes, American sizes, English sizes, Spanish sizes, and almost everything else except Assyrian sizes.

Beyond that, different standards are often employed for different brush types, even by the same manufacturer. And a size 6 flat from in one label may not match the same size from a different maker, even in the same type brush.

Sometimes it's confusing to us, and it must be doubly so for beginners. We can only offer this suggestion: If you're taking a class, ask the instructor either to specify in both numerical and "inch" terms, or to say something like "Brand X Size 6 Flat or equivalent."

A particular area in which to be skeptical is in the realm of extremely small sizes. We've seen many a 10/0 brush that was actually smaller than a 20/0 offered by another maker. We're totally convinced that in some cases these mini brushes are so-marked simply as a marketing ploy, rather than reflecting true size differences.