Oki 4837 Fabric Ribbon Black 2496 for use with 520/521. Install a genuine OKI ink ribbon in your ML520 or 521 Microline dot matrix printer for top quality monochrome black results. This ribbon is designed for an easy changeover for quick installation. The high quality nylon construction ensures minimal wear, offering a lifespan of up to 4 million characters per ribbon. It uses premium-quality inks with a metered output for consistent quality, precisely controlled to ensure even coverage for each and every character.