C = 300 series stainless steel. Passivated and/or tested per ASTM A380. A = Aluminum. Plain finish. Type: IU = Ultrasonic/thermal, ered IUT = Ultrasonic/thermal, straight wall IUTF = Flanged, ultrasonic/thermal, straight wall IS = Ultrasonic/thermal, symmetrical I = microPEM, Ultrasonic/thermal, symmetrical IB = Molded-in, blind threaded