Plastic refill is designed for use with PM Company Klipboard Keeper with Pen, Preventa Antimicrobial Necklace Pen, Versatile Ergo Triangular Coil Pen, & Preventa Triangular Coil Pen. Offers high-density, acid-free, water-resistant ink. Cross-reference marks are designed for easy identification. Simply find your pen cross-reference mark, & snip off.