0.5 mm. Rubber grip. Rolling ball. Retractable. Refillable. America's No. 1 selling gel pen (Source 2008/2009 AC Nielsen).Discover writing perfection! Dynamic Gel Ink Formula: An exceedingly smooth writing, smear-proof gel in pen. Retractable: No cap to lose. Contoured Rubber Grip: Comfortable finger-friendly design. Refillable for Continued Use: Use the G2 refill. Made in Japan.