ABSTRACTAn inexpensive and simple mechanical size grader for freshwater prawns was developed, utilizing a pair of diverging rollers (114 mm diameter and 90 cm length). Five machine variables were studied using a two‐level fractional factorial sequential search technique. Optimum roller speed was 100 RPM, with an optimum roller incline of 10 percent. Space between rollers was 20 mm at the entrance and 29 mm at the exit. At a recomnended feeding rate of 3 prawns every 3 seconds, 90 percent correct sorting of market sized prawns was achieve