This stainless steel calligraphy nib unit is compatible with the fountain pens listed under Compatible Products. To replace the nib of a pen whose grip section matches the one included with this nib unit, unscrew the old grip section from the barrel of the pen and screw in the replacement nib unit.
To replace the nib of a pen whose grip section does not match the one included with this nib unit, use your fingertips to grip the top of the old nib and the feed of your pen and pull them straight out from the grip section of the pen. Then, pull the calligraphy nib and feed out of the replacement unit's grip section and insert them into the pen's grip section.
The video features the 1.1 mm Kaweco Calligraphy Fountain Pen Replacement Nib found here.