This is a 4" x 12" vent length for the Rinnai R98i Series tankless water heaters.  Manufactured by ProTech, their FasNSeal® line of vent kits are made from AL29-4C® which is a superferritic stainless steel designed for extreme resistance to chloride ion pitting, crevice corrosion and stress corrosion cracking, as well as general corrosion in oxidizing and moderately reducing environments. 

Each vent length and component features a built-in mechanical locking band and gasket.  Parts are simply pushed together to a stop bead, which renders the joints air and water-tight.  By tightening the integrated mechanical locking band, parts are fastened together in seconds.  FasNSeal® can be taken apart and reassembled in minutes, making inspection, maintenance or rerouting of FasNSeal® systems a breeze.