Two foam inserts for the Elite Mini Internal Filter. The foam does both the mechanical work and, more importantly, carries the bacteria that process ammonia — which is why it should be squeezed out in a jug of tank water rather than replaced on a schedule.
When to replace rather than rinse — when the foam no longer springs back after squeezing, or has torn. Replace one insert at a time and leave the other in place for a few weeks, so the filter does not lose its whole bacterial colony at once.
Hagen has used two part-number families for Mini filter foam. This is the insert for the current Elite Mini Internal Filter; the older Mini filter takes the Mini filter replacement media.
More Hagen Elite spares: Hagen Elite at PeekAPaw · Fish & Aquarium Supplies