What printers can use HP 21 cartridge?

The HP 21 cartridge is compatible with several HP inkjet printers, including the HP DeskJet 300 series, DeskJet 500 series, and some models in the HP OfficeJet series. Specific models include the DeskJet 3520, 3740, and 3840, as well as the OfficeJet 4110 and 4215. Always check the printer's specifications or user manual to ensure compatibility before purchasing a cartridge.