Uni-Ball Eye Rollerball Medium Tip Pen Black Twin Blister Pack, Pack of 6. The best selling Uni-Ball Eye Rollerball pen contains liquid ink that is fade and water resistant. Featuring a stainless steel precision tip, this pen ensures a smooth writing experience. Each retail pack contains 2 black pens with a medium tip to write a neat 0.5mm line. The see-through barrel allows the user to view the ink level during use.