HP No. 21 Black Ink Cartridge (c9351a)

As with all original cartridges (like those shown above) from Inkraider, our compatible replacement cartridges are brand-new, unopened and were designed specifically for certain printer models. The single biggest difference between an original cartridge and a compatible replacement cartridge is the manufacturer. An original cartridge is manufactured by the same company who designed and built your printer, whereas compatible replacement cartridges are manufactured by companies that don't have their own range of printer models, and so manufacture cartridges for the printer models of other brands. Due mostly to consumer unfamiliarity, cartridges offered by these brands are often significantly cheaper than their original counterparts. In addition, compatible replacements can be mixed with original cartridges in your printer in any way you like, no matter how full the remaining original cartridges might be. Please note however, that using cartridges from a number of different manufacturers may result in a temporary degrading of your printer's output quality.