Pilot Hi-Tec-C Coleto Gel Ink Pen Refill 0.3mm Aqua Blue/Size: Maximum diameter 3.1mm x Length 126mm/Core size: 0.3mm ultra-fine point type/Water-based biopolymer ink/Features: Choose your preferred replacement core and set it into the Coleto pen body. With a variety of replacement cores, you can enjoy different writing styles.