Pilot Frixion Roller Ball Pen, BlueBlue ink, erasable roller ball pen with a 0. 7 mm tip. Its thermo sensitive gel ink writes smoothly and can be erased cleanly by friction (via the built in eraser), making it great for notes, drafts, crossword sudoku, diary entries or schoolwork. The pen has a comfortable rubber grip and a retractable tip but because the ink can vanish, its not suitable for signatures or permanent documents.