High-performance removal type water purifier cartridge JF-21, easy replacement. - Type: High-performance removal type - Model Name: JF-21 - Usage Notes: Replacement is required approximately every 4 months when using 10 liters of water per day. - Replacement Method: Easy installation instructions are included. - Brand new, unopened Although brand new and unopened, it is unused because the model number was different when I tried to use it after opening. Thank you for looking.