Pen UNO is perhaps the most minimal writing instrument in the market. Created by Ensso, the space-grade aluminum pen was designed to be a pleasure to write with and beautiful to look at. With only 5.3 mm in diameter, Pen UNO is one of the slimmest pens ever manufactured, yet it is very comfortable to use because its holding barrel (also doubles as a twisting cap) is slightly wider. Weighing about the same as a standard pencil, the sleek and super minimal pen uses Hi-Tec C Coleto gel ink cartridges which are widely available in a variety of colors and lineweights. Available in five iPhone-matching shades: space grey, black, silver, gold, and rose gold.