All green coffee is bought with a screen size reference. This is a process where a set amount [we use 300g] of green coffee is passed through a series of interlocking trays placed one on top of the other. The largest screen size  is on the top, smallest size  on the bottom. The screens are shaken vigorously by hand and beans are either retained by the screens or fall through the various screens. Retained beans in each tray counted and a percentage can be worked out of each different screen.
Whys is screen size important ?
Consistency in roasting.