Code- 421 (Green top) is an 'Axial' cartridge meaning the water enters at the base and travels along the length of the filter.
It has a 1 micron pre filter at the base to prevent dirt.
Following this is the SilverSafe, to kill bacteria that may otherwise breed in the carbon. The carbon removes the contaminates.
The final process is another bed of SilverSafe to assist in maintaining a bacteria free environment in the purified water.
Please note: This cartridge does NOT fit the B.E.S.T. Inline models.
This cartridge is for 'domestic style' systems that fit 9 & 3/4" sized replacement cartridge. Does not fit the B.E.S.T. Inline models.