It's one of the slimmest writing tools around. Yet it's also perfectly comfortable. The Pen Uno achieves this feat by augmenting its 5.3mm body with a wider holding barrel that doubles as a twisting cap. It's helped along by the anodized aluminum construction, which makes it remarkably strong yet keeps its weight down to about that of a standard pencil, and by the Hi-Tec-C Coleto gel ink cartridges that were originally designed for use in multi-color pens. It's available in four iPhone-matching shades, with the special-edition black version reserved for those ordering a full set of four.