Frixion Ball Knock Design Series LIMITED 2015 This product was released as a limited edition in 2015. The ink disappears when rubbed with the rubber on the top of the pen. Ink Color: Black Ball Diameter: 0.5mm (Extra Fine) Erasable Ballpoint Pen Erasable Pen I tested it out, and all the pens write. Although it is a new, unused item, please refrain from purchasing if you are concerned about home storage.