Madison is the only pen model within Osprey pen offerings that is available with a Size 6 Ultra-flex Steel nib. The nib is friction-fit with an ebonite feed, directly into the outer section of the pen. This outer section does not have internal threads and hence cannot accept any interchangeable nibs.

In order to use the entire range of Osprey nib unit offerings, namely #6 Steel, #6 Gold, #5.5 Ultra-flex,  Zebra G and Phosbronze flex, you will need a second Madison section called the Madison2 Section, that has internal threads to accept the interchangeable nib units. Make sure to get Madison2 Section if you don't already have one.

For Size 6 Ultra-flex replacement nib units, check out Madison replacement Nib Unit item listing.