Uni-Ball Impact Gel Pens contain a smooth flowing gel ink which delivers bold, vibrant colors that stand out from the page. Each pen has a soft grip which keeps you comfortable while you're writing. Each pen contains a 1.0 mm size nib. They're perfect for detailed, precise and controlled writing and drawing. Each pen contains smooth flowing gel Black ink thanks to the twin-ball mechanism which prevents ink back-flow. You can refill this pen using a Uni-Ball 153S Gel Pen Refill.