This is a Maytronics Super Ultra-Fine Filter Basket (Small) for several Dolphin pool cleaners including the Active Series. This filter basket has super ultra-fine filter panels.
The super ultra-fine filter basket is designed for the Active, 10, Active 15, S50, S100, T15, T25, Prowler 910, Prowler 917, Warrior SL, Echo, Saturn, Cayman, E10, Escape, Nautilus CC, Encore, Proteus DX3, Solo, Advantage, and Explorer E20.