Gel-type Zebra pen and tip thickness 0.5mm - 0.7mm - 1.0mm. Gels have a range of ink colors and bright writing. The ink is more fluid, so they "roll" more comfortably and require less pressure, but they can smudge.
Zebra rollerball pen set, with colorful ink. Rollerball writing is similar to that of a pen. They produce the most ink compared to other types, they are comfortable to write, they don't leave gaps, but they can smudge. Not suitable for low quality paper.