The Fluval A343 is an aquarium filter insert that is designed to fit the following:
The Fluval 2 - Aquarium Carbon Filter Insert - 3-Pack traps large amounts of particulate and liquefied waste from aquarium water. This Fluval carbon cartridge features a double-fused sheath design that traps solid waste before it can clog the fine pores of the powderized carbon layer, permitting higher adsorption for a longer period of time. This replacement aquarium filter comes in a 3-pack.
The Fluval A343 specifications: