Enhance your fountain pen writing experience with high-quality Black Ink Cartridges. These refillable ink cartridges, with a diameter of 2.6mm and 3.4mm, are compatible with a variety of general purpose fountain pens. Each package includes 20 pen ink sacs for long-lasting use. Made of durable plastic, these standard type nibs provide a smooth and clean writing experience. Suitable for students and professionals alike, these Blue Black Refill Ink Fountain Pen Ink Bags are the perfect universal addition to your pen collection.