The Canon BCI-21 color ink tank is designed to work as part of the BC-21e cartridge system. The BC-21e cartridge contains the print head and two separately replaceable ink tanks: one is the BCI-21 color ink tank (also known as BCI-21C or BCI-21clr), and the other is the BCI-21 black ink tank (also known as BCI-21B or BCI-21Bk). This system allows you to simply replace the appropriate ink tank when it runs dry, without having to replace the entire cartridge. Pretty smart. Canon utilizes this print system in the following models: BJC-2000, BJC-2010, BJC-2100, BJC-2110, BJC-2115, BJC-2120, BJC-2125, BJC-4000, BJC-4100 Series, BJC-4200 Series, BJC-4300 Series, BJC-4400, BJC-4550, BJC-5000, BJC-5100, MultiPASS C2500, MultiPASS C3000, MultiPASS C3500, MultiPASS C5000, MultiPASS C530, MultiPASS C545, MultiPASS C5500, MultiPASS C555, MultiPASS C560, and MultiPASS C635.
