...be sure you do not throw away the metal plugs, you need them to convert Sharpie retractable pens for use in the Bid Idea pen. These are great cartridges and can easily be refilled/restored by removing the plug and adding alcohol based marker ink to the markers and Noodler water based dye Highlighter ink to highlighters. Note that the two types of inks are not interchangeable and markers use alcohol based ink while highlighters use water based ink. Using the wrong ink will destroy your cartridge.