What is the difference between flexible connectors and steel bellows?

Flexible connectors consist of a 321 stainless steel hose terminated with couplings or flanges. They are generally between 18″-24″ long, and designed to absorb vibration between the engine exhaust manifold and the engine silencer. Steel expansion bellows feature a single-ply or multiple-ply corrugated 304 or 321 stainless steel construction, and are specifically designed to absorb axial movement. While flexible connectors allow 0.25″ axial deflection per 12″ length, an expansion bellows often provides 1.5″-3″ deflection in a 12″ length. We recommend the installation of flexible connectors at the engine outlet connection. Expansion bellows should be installed in piping downstream of the silencer, where the piping changes direction.