This is an exhaust resonator for Cummins Onan KY RV Generators. It softens exhaust noise and reduces sound levels in some installations up to one dB(A). It is constructed of aluminized steel. It mates with standard 1-1/2" O.D. exhaust pipe. Installation requires a 1-1/2 inch (38mm) O.D. pipe clamp (Part # 155-1015, sold separately).