Abstract: A clip attaching structure includes a clip supporting portion which protrudes on an outer circumferential surface of a main body, a clip, and a coil spring. The clip is configured to be rotatable with respect to a fulcrum at which the clip is engaged with the clip supporting portion. The convex portion is inserted into an inside of one end portion of the coil spring, and the other end portion of the coil spring abuts against the outer circumferential surface of the main body. A base portion of the convex portion has an outer diameter greater than an inner diameter of the coil spring, and a tip end portion of the convex portion has an outer diameter smaller than the inner diameter of the coil spring.

Abstract: An oil-based ink composition for a ballpoint pen has an ink viscosity at 25° C. is 200,000 mPa·s or more at a shear rate of 0.019 s?1 and 5,000 mPa·s or less at a shear rate of 10,000 s?1 and a storage modulus at an angular frequency of 0.019 rad/sec is 10 Pa or more. The ink composition ensures a thin-width writing line, without bleeding or feathering, and prevents ink-depleted regions at the central part of the writing line so that the writing line is uniform and clear.

Abstract: A clip attaching structure includes a clip supporting portion which is protruded on an outer circumferential surface of a main body, a clip, and a coil spring. The clip is configured to be rotatable with respect to a fulcrum at which the clip is engaged with the clip supporting portion. The coil spring is provided being closer to one end portion of the clip than the fulcrum, and biases the other end portion of the clip to make the other end portion abut against the outer circumferential surface. The clip has a convex portion which is protruded towards the outer circumferential surface of the main body. The convex portion is inserted into an inside of one end portion of the coil spring. The other end portion of the coil spring abuts against the outer circumferential surface of the main body.