Pentel Hybrid Gel Grip RTX Retractable Gel Roller, Medium Line, Permanent Black Ink, Box of 12 (K157-A) Durable 0.7mm metal tip delivers smooth medium lines Brilliant ink is smooth, permanent and acid-free Unique comfort grip makes writing a pleasant experience Unique "pocket-proof" system prevents unwanted ink marks Conveniently refillable with Pentel KFR7 medium refill