When selecting pen refills, identify the pen manufacturer and model, check the size and shape of the existing ink cartridge, and find a refill that matches these characteristics. Check whether there are quantity and shipping promotions and buy refills in bulk to ease the process of procuring future refills.
Some pens can take standard refills while others require the refill cartridges specified by the manufacturer. To find the right refill, look for cartridges that have the same size and shape as the cartridge of your existing pen. Ensure that the identified refills are made for the type and model of your pen. Although a rollerball refill and a fountain pen refill may be from the same manufacturer, they may not require the same refill. Check the tip size of your pen, and ensure that the refill does not have a wider or narrower tip than the one you are used to.
If buying a refill online, pay attention to the refill color as computer screens may not show the color shade correctly. For example, blues and blue-blacks are easy to mistake. Check the listed characteristics to ensure you buy the refill you intended to get. Consider ordering refills with multiple colors and tip sizes to explore new ways of writing.