MILLTEK SSXBM1010 Cat-back Twin 76.2mm GT76 BMW 4 Series F32 428i Coupé (automatic and without tow bar and N20 Engine Only)Description MILLTEK SSXBM1010 Cat back Twin 76. 2mm GT76 BMW 4 Series F32 428i Coup (automatic and without tow bar and N20 Engine Only) The Cat Back systems are designed as direct replacements for the original exhaust, offering improved sound and aesthetics. Multiple configurations are available, allowing the owner to select the desired increase in exhaust volume or a more aggressive tone. All products are manufactured from 304L aircraft grade