Thank you for viewing. This is a Montblanc-compatible oil-based ballpoint pen refill. It is approximately 98mm long and 6mm in diameter, and can be used in current oil-based ballpoint pens, but adjustments are required for the knock-type S-line pens. If you have any questions, please feel free to comment. In addition to the Montblanc type, we also carry Cross-type and Parker-type refills. The Montblanc type also has water-based rollerball refills in addition to oil-based ones. Ink colors are black and blue. Cross and Parker types also have red. Combinations are also possible, so please feel free to inquire in the comment section.