... FO. MODEL NO.-. BOB-180/30-2P ; PLASTIC IMPELLER/ 2POLE-. BOB-190/45-2P, 2S ; STEEL OR PLASTIC / 2,4 ... POLE-. BOB-225/50-2S,4S ; STEEL IMPELLER / 2 ... , 4POLE-. BOB-250/50-2S,4S ; STEEL/ 2, 4POLE-. ... BOB-280/50-2S,4S ; STEEL / 2,4POLE BACKWARD FAN ...