A refill for writing implements has an ink reservoir tube (1) made of resin material and formed to be a straight cylinder and a writing tip (2) attached to one end of the ink reservoir tube (1), and a value of an expression of D.sup.4(D2t).sup.4 is selected to be 45 or greater, where D denotes an outer diameter of the ink reservoir tube (1) and t denotes a thickness of the ink reservoir tube (1). It is possible to secure the necessary storage amount of ink in the ink reservoir tube (1) without increasing the outer diameter thereof, and is also possible to provide a refill for a writing implement and a writing implement which allow one to keep writing comfortably without feeling of discomfort in writing.

A multi-function writing implement includes a pen shaft, a colored pen assembly, and an erasing pen assembly. The colored pen assembly is arranged at one end of the pen shaft. The colored pen assembly includes a cartridge seat, a nib seat, a plurality of colored cartridges, a plurality of relay cartridges, and a plurality of colored ink cotton tubes. The erasing pen assembly is arranged at the other end of the pen shaft opposite to the colored pen assembly. Only one end of the pen shaft may have at least two colors for providing the user to use different colors and the user is not necessary to use two nibs respectively arranged at two ends of the pen shaft by replacing in turn.

A multi-function writing implement includes a pen shaft, a colored pen assembly, and an erasing pen assembly. The colored pen assembly is arranged at one end of the pen shaft. The colored pen assembly includes a cartridge seat, a nib seat, a plurality of colored cartridges, a plurality of relay cartridges, and a plurality of colored ink cotton tubes. The erasing pen assembly is arranged at the other end of the pen shaft opposite to the colored pen assembly. Only one end of the pen shaft may have at least two colors for providing the user to use different colors and the user is not necessary to use two nibs respectively arranged at two ends of the pen shaft by replacing in turn.

A composite writing implement according to an embodiment includes a barrel, writing shafts housed in the barrel, a cam main body including a cam projection, an end surface extending along the cam projection, and a latch recess provided in the cam projection, and sliders configured to be connected to respective rear ends of the writing shafts, and include a cam configured to be latchable to the latch recess, and have a sliding contact surface to be pressed against the end surface, wherein the end surface includes a first inclined portion that is positioned on the front end side of the cam projection and is inclined by a first incline angle, and a second inclined portion that is positioned further toward the rear end side of the cam projection than the first inclined portion, and is inclined by a second incline angle that is larger than the first incline angle.

A composite writing implement according to an embodiment includes a barrel, writing shafts housed in the barrel, a cam main body including a cam projection, an end surface extending along the cam projection, and a latch recess provided in the cam projection, and sliders configured to be connected to respective rear ends of the writing shafts, and include a cam configured to be latchable to the latch recess, and have a sliding contact surface to be pressed against the end surface, wherein the end surface includes a first inclined portion that is positioned on the front end side of the cam projection and is inclined by a first incline angle, and a second inclined portion that is positioned further toward the rear end side of the cam projection than the first inclined portion, and is inclined by a second incline angle that is larger than the first incline angle.

In one embodiment, a writing instrument refill includes a first portion having flexibility, and a second portion having a cross-sectional area larger than a cross-sectional area of the first portion, wherein the center of figure of the cross section of the first portion is offset from the center of the figure of the cross section of the second portion, the first portion and the second portion are formed integrally, and a part of the first portion has an outer diameter smaller than an outer diameter of the other part of the first portion.

In one embodiment, a writing instrument refill includes a first portion having flexibility, and a second portion having a cross-sectional area larger than a cross-sectional area of the first portion, wherein the center of figure of the cross section of the first portion is offset from the center of the figure of the cross section of the second portion, the first portion and the second portion are formed integrally, and a part of the first portion has an outer diameter smaller than an outer diameter of the other part of the first portion.

A refill for a writing tool includes an ink containing tube that is made from a resin material and formed in a straight cylindrical shape, and a writing tip that is attached to an end of the ink containing tube. A press-fit portion, formed at the end of the ink containing tube, has a thickness being made thickened toward an inner circumferential surface and has an opening hole penetrating in an axial direction at a central portion of the press-fit portion. The writing tip or a relay member supporting the writing tip is press-fitted and attached to the press-fit portion. The refill for a writing tool can ensure a necessary and sufficient amount of ink stored without expanding an outer diameter of the ink containing tube, and sufficiently secure mechanical strength of an end portion, and a writing tool using the same can be provided.

A refill for a writing tool includes an ink containing tube that is made from a resin material and formed in a straight cylindrical shape, and a writing tip that is attached to an end of the ink containing tube. A press-fit portion, formed at the end of the ink containing tube, has a thickness being made thickened toward an inner circumferential surface and has an opening hole penetrating in an axial direction at a central portion of the press-fit portion. The writing tip or a relay member supporting the writing tip is press-fitted and attached to the press-fit portion. The refill for a writing tool can ensure a necessary and sufficient amount of ink stored without expanding an outer diameter of the ink containing tube, and sufficiently secure mechanical strength of an end portion, and a writing tool using the same can be provided.

A multicolor writing instrument with an automatic return function includes a lower housing having a hollow cylindrical shape; an upper housing connected to an upper portion of the lower housing and formed with locking steps; a clip member hingedly provided on the upper housing so as to be movable about a hinge shaft; a coil spring resiliently installed between the clip member and the upper housing; pen cores filled with at least two different color inks; knobs having ends fitted into the respective pen cores; return springs resiliently installed between the pen cores and the knobs; and a return member formed integrally with the clip member on one side of the hinge shaft and toward the respective knobs.