Our overfeed is a device that rests on top of a flexible nib. It is designed to let you draw wider lines for a longer period of time using the flexible pointed nibs we support in our pens.
Your pen must be configured for overfeeds if you want to use an overfeed. You can replace the overfeed with a spacer when you don't want to use the overfeed, but we don't recommend doing this often. You should have the right size tools and be handy with them.