Current models of Retro 1951 mechanical pencils use 1.15mm lead. We have that as well as erasers. Some older models of pencils with engraving on the nose cone will fit .9mm lead.
Retro Hexomatic pencils fit .7mm lead and use the small erasers shown below.
If you have the Retro Twin Pen, it fits 2-5/8" mini ballpoint refills. We offer Monteverde liquid ink mini ballpoints.
If you're unsure about exactly what you need, please give our refill experts a call at 800.766.7367