A: Silk quality is graded on several qualities and characteristics such as denier, evenness, cleanliness, tenacity, elongation etc. Silk qualities first get graded with a letter grade of A, B, or C (A being the best). Then they can get a number rating 1-6. 6A is the finest quality of silk available but it is very rare and the most expensive to buy. This is the quality of silk that is often used in surgical procedures for sutures. 5A is likely the finest quality of silk made for clothes.