Feature:1. Ink cartridge length: 50mm; Cartridge outer diameter: 5mm; Bore diameter: 3.4mm.2. Suitable for most fountain pens. Please make sure your pen fits our ink according to the size information.3. Easy ink change without dirty hands. These ink cartridges are not erasable.4. Smooth and even ink output, enjoy a smooth writing experience.5. Suitable for office, school, home use.Specification:Features:Ink cartridge length: 50mm; Cartridge outer diameter: 5mm; Bore diameter: 3.4mm.Suitable for most fountain pens. Please make sure your pen fits our ink according to the size information.Easy ink change without dirty hands. These ink cartridges are not erasable.Smooth and even ink output, enjoy a smooth writing experience.Suitable for office, school, home use.Specifications:Ink Color: Dark Blue/Black/Red(optional)Quantity: 50pcs/100pcs(optional)Ink Cartridge Length: 50mmCapacity of Each Piece: 0.9mlCartridge Outer Diameter: 5mmCartridge Inner Diameter: 3.4mmPacking List:50 * Ink CartridgesPackage List:50 * Ink Cartridges