The Fluval A66 fits the following:
The Fluval A66 Elite Foam Water Filter for A60 5-pack includes five replacement aquarium filters for the Elite A60. The Elite aquarium filter removes debris in aquarium water and encourages the growth of beneficial bacteria populations. This foam aquarium filter provides very efficient mechanical filtration for your aquarium.
Fluval A66 Elite Foam Water Filter for A60 5-pack specifications: