Abstract: In a writing device, an engaging portion having an annular protrusion and an annular depression is formed on the outer surface of the head end portion of a writing device body. Also, an engaging portion having an annular protrusion and an annular depression is formed on the outer surface of the tail end portion of the writing device body. A plurality of engaging protrusions are formed on the inner surface of a cap arranged at a predetermined spacing in the circumferential direction of the cap. When the cap is attached to the writing device body, the engaging protrusions move over the head end side annular protrusion and then engage with the head end side annular depression. When the cap is attached to the tail end of the writing device body, the engaging protrusions of the cap move over the tail end side annular protrusion and then engage with the tail end side annular depression. As a result of the engagement, the cap is less likely to unintentionally come off the writing device body.

Abstract: The tubular main body of a writing instrument has a cylinder the writing end of which is formed to include a cap-fitting portion. A gripping portion, which is formed on the cylinder below the cap-fitting portion, has an outer peripheral surface provided with a number of annular slip-preventing grooves. A cap detachably fitted on the cap-fitting portion of the cylinder includes a clip extending axially to a point in the vicinity of the gripping portion. The clip has an engaging projection formed on an underside thereof for engaging one of the slip-preventing grooves of the gripping portion when the cap is attached. When the writing instrument is clipped to the fabric on the outer side of a shirt or jacket pocket, the engaging projection on the clip and the slip-preventing groove of the gripping portion on the cylinder of the tubular main body engage each other via the fabric clamped between them.

Abstract: A writing instrument in which plural cartridges are fitted and coupled in series with each other in their longitudinal direction so that the cartridges are removable from each other. Each of the cartridges comprises a tubular body having a tubular projection at one end of the tubular body and having an optionally shaped cross section, and a core unit inserted in the tubular projection so that the core unit is held in it. The tubular body has an insertion hole into which the tubular projection of the adjacent cartridge, which is coupled to the tubular body, is fitted in the longitudinal direction of each cartridge so that the tubular projection is held in the insertion hole removable from it. The former tubular projection has an insertion hole in which the core unit of the adjacent cartridge is housed.