The CLI-521BK is a black inkjet cartridge that contains pure black ink for different uses. The pure blacks that the cartridge outputs gives a great definition of blacks in all of your prints. These include text printouts, documents, and even photos which receive a higher definition through the blacks. The cartridges are applicable in different places, such as at home, or in businesses. They come in an 11.5ml cartridge that is completely filled with high yield ink to give you consistent and constant jet black colours. The black cartridges are compatible with several different canon printers to give you definite, vivid colours. The compatible printers are the following: Canon IP 4600, Canon IP 3600, Canon MP 620, Canon M 540, Canon MX 860, Canon MP 550, Canon MP 560, Canon IP 4700, Canon MP 980, Canon MP 630, Canon MP 640, and the Canon MP 990.