O-Ring Part Number: A20063 / A20064 (2-Pack) [also known as A-20063 / A-20064] Compatible with Fluval 304, 305, 306, 307, 404, 405, 406, 407 canister filters. The A20063 O-ring is designed to seal the motor head/lid to the filter canister for the models listed above. This pack includes two (2) O-rings (also referred to as seals or gaskets). Replace your leaking O-ring and keep a spare for future use with this convenient 2-pack. If you have any questions please do not hesitate to contact us