Empty markers can come in many configurations. But the two most common Empty markers are valve actuated markers and Mops.
Valve actuated markers have a rigid barrel, internal valve and a felt nib. This empty marker is commonly used as a pump action paint pen, but a variety of formulas can be put into them. These are best suited for high flow paints, inks and adhesives.
Mops are an empty marker that features am empty barrel with a duber style felt pad for a nib. These also can have the more durable mohair type. These are great for thicker paints, primers and etching compounds.