There are 4, U.S. Grades, U.S. Fancy, U.S. Extra No.1, U.S. No.2.  The principal trading grade is U.S.1, even though in California there is an emphasis on marketing toward the top grade or better.

U.S. No.1 consists of nectarines of one variety which are mature but not soft or overripe.  They must be well formed, clean and free from decay, broken skins which are not healed, worms, worm holes, and free from injury caused by split pit, and free from damage caused by bruises, growth cracks, hail, sunburn, spray burn, scab, bacterial spot, scale, scars, russeting, other disease, insects of mechanical, or other means,  At least 75 percent of the nectarines in any lot shall show some blushed of red color, except for the John Rivers variety.