The PG uses four roller with flats on the top set to separate the shrimp. The top set vibrates the shrimp to stop them from stacking up on top of one another. This stops small shrimp from riding a larger shrimp down to the wrong grade. Both the rollers and the grade chutes are adjustable in order to allow for each customer to customize the grades for their needs. The standard size of the graders is from 1 to 6 channels.