These special revisions of the HP 304XL ink cartridges have been designed to work with the most recent HP firmware. When producing these remanufactured Hewlett Packard cartridges they have focused specifically on the Deskjet and Envy printers listed as compatible, that we were previously unable to offer cartridges for.Remanufactured Hewlett Packard ink cartridges like the N9K07AE found here, retain as much print quality as possible and lessen the environmental impact of your printing. All the genuine Hewlett Packard mechanical parts are retained and the empty cartridge is then refilled with a top-quality HP 304XL cyan, magenta and yellow ink. The completed remanufactured N9K07AE ink cartridge is then thoroughly tested by our manufacturers. The attention given to the N9K07AE during refilling means it remains compatible with all the same thermal inkjet printers including the HP Deskjet 3720. Like all our products, the remanufactured HP 304XL colour ink cartridge comes fully guaranteed and is covered by our 100% satisfaction guarantee