CAUTION: Using a non-OKI ribbon may damage the printhead and void any warranties. -Black Ribbon, self inking cartridge for ML420/421 and ML490/ML491 24-pin printers. -Average 7.5 million character life. -Material: Nylon fabric, cartridge type, re-inking -Type: Black Ribbon To protect your investment longer after the warranty has expired, use only genuine Oki Ribbons. Why take chances? Use the ribbon that was designed by the same engineers who designed your printer; manufactured to precise tolerances to eliminate binding and wear on the ribbon drive mechanism and the highest quality ink used to reduce friction and premature printhead wear.