Abstract: A pen system comprising a cover member joined to an adapter having an anterior end of an ink cartridge disposed therein is disclosed. A pen housing covers the ink cartridge and is sealed via a plug. In one embodiment, a slit divides a surface of the adapter to allow a collapse of the adapter, thus narrowing a height of the adapter, to allow insertion of the adapter into the cover member. A first and second annular groove are disposed at a center of the adapter, where each annular groove interfaces with a cover member annular ridge to define an open and closed position of the pen. In an alternate embodiment, an annular washer having an annular ridge is disposed in the cover member, in place of the cover member annular ridge, to interface with the first and second annular groove thus defining the open and closed positions of the pen.