| 摘要 |
PROBLEM TO BE SOLVED: To provide a writing material capable of fitting and releasing a cap very easily. SOLUTION: One side between the outer peripheral engaging part 10a of tip end side of a barrel 10 and a part 20a, to be engaged with the part 10a and positioned on the inner surface of a cap 20, is provided with substantially isosceles triangular chevron parts 11 while the other side is provided with substantially isosceles triangular trough parts 21 similar to the shape of the chevron parts 11. Two pieces of the chevron parts 11 are arranged symmetrically about the axial center of the barrel whereby respective chevron parts are formed with a predetermined space along the peripheral direction of the barrel while four pieces of trough parts 21 are formed with an equal space so as to be engaged with the chevron parts 11. The height of the chevron parts 11 from the trough to the apex thereof and the depth of the through parts are specified so as to be a value operated by the formula of πR/4 substantially when the radius of the outer periphery of the engaging part 10a is shown by R. |
