Ballpoint Pens by OHTO. Details:Retractable oil-based ballpoint pen. The best feature is a retractable ballpoint pen on the thinnest axis in the world. The total length of 0.4 inch (9.1 mm) x maximum diameter 0.2 inch (5.2 mm), and the total length is about the same length as business cards. Unknock activated by side button The tip is narrow as a needle point. The ink is an improved oil-based ink that is lower viscosity and smoother and produces crisp lines. Comes with a convenient holder (W60 mm x H91 mm) for portability. Business card size allows you to insert it into a business card case or notepad as a bookmark and always carry it with you. This unique ballpoint pen is useful for emergencies. Please use auto R-4C5NP croodile refills. Other products may not fit the product. If you lose the spring inside the main unit and the adapter attached to the top of the core, it will not be able to knock it, so be careful not to lose it.