Used in about 90% of all the world's ballpoint pens, the "Parker-Style" ballpen refill is named after the Parker brand that made it so popular. Since it is so widely used, several manufacturers produce the same model refill which is compatible with most click-top and twist-action ballpoint pens. It is distinguishable by its slender tapering toward the tip and the plastic back-end piece that is uniquely shaped to fit most common ballpoint pen mechanisms. This new Monteverde USA Capless Ceramic Gel refill allows you to convert your ballpoint pen into a Capless Rollerball. The Monteverde USA refill offers: For the first time ever this refill offers a combination of a ceramic ball with gel ink Finest developed inks Stainless steel tip with ceramic ball Note: If you are unsure which refill may fit into your pens, you may visit our WorkRoom for fitting purpose.