Cylindrical sponges cover the inflow holes of filter pipes to prevent tiny animals from getting sucked in and trap particles and debris. They also function as small bio filters.
Small: 1 cm inner diameter, 2" length
Medium: 1.5 cm inner diameter, 2.75" length
Large: 2 cm inner diameter, 3" length
The sponges stretch so they should work for pipes that are +/- 5mm from the inner diameter of the sponge.