Click pens are usually ballpoint pens. They operate by clicking the top or moving the bolt type click to extract the ink chamber.
Fountain pens use either an ink cartridge or an ink pump to pump ink from an ink well.
Inlay Pens are also ballpoint. This is where you can select from available kits representing your choice. Be advised that not all inlays fit all pens. We can discuss this if you have a choice. Most of the inlays can also be applied to certain keychains.
Military Pens are available as inlays or as a clip. Be advised that the clips will not fit all pens.