Overall Dimensions 3 1/2 IN. X 2 IN. Bio Wheel Assembly for Penguin 125 Filter. The Bio-Wheel bracket is sold separately. The Penguin Filter eliminates toxic ammonia on contact. Replacement bio-wheel assembly. A classic wet/dry biological filtration & more, because it is only expose to prefiltered water it does not clog & never need. Eliminates toxic ammonia on contact, create higher levels of oxygen, more stable ph & a healthier environment.