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US standard sieves are used to screen beans for grade standard specifications. The United States Department of Agriculture (USDA) standards for dry beans (USDA 2017a) state that “well‐screened” beans “shall mean that the beans are uniform in size and are practically free from such small, shrivelled, underdeveloped beans, splits, broken beans, large beans, and foreign material that can be removed readily…through use of sieves.” Sieves are to be constructed of 0.319‐inch‐thick metal with perforated round holes. Sizes are specified as a 30/64 sieve (0.4687 inch on a 11/64‐inch center); a 28/64 sieve (0.4375 inch on 19/32‐inch center); and a 24/64 sieve (0.0319 inch on a 17/32‐inch center). All rows of perforations are to be staggered. The screening is conducted in commercial operations (see ssss1), and these sieve specifications are used during USDA grading procedures to the assess sample uniformity for size.

Commercial market classes have characteristic seed shapes that range from spherical to elongated (e.g., navy beans are generally characterized by a small round seed whereas kidney beans have elongated seed that resemble the human kidney). Similar to seed size, seed shape is under genetic control; however, deviations may occur due to stressed growing conditions (i.e., water availability and temperature profiles throughout the growing season).