There is provided a friction body which is adapted to rub a thermochromic image or handwriting formed on a paper surface by use of thermochromic ink to thermally discolor the thermochromic image or handwriting by frictional heat resultant from rubbing, a thermal conductivity of a friction portion of the friction body is set to be within 0.05 W/(m.Math.K) to 50 W/(m.Math.K).

A protective element for a writing tip of a writing instrument including a cap extending longitudinally along a central axis and configured to be fitted onto a body of the instrument, and a clip extending substantially parallel to the central axis from a first end fixed to the cap to a free end. The clip and the cap are in one piece.

A retractable ink pen including an elongate ink cartridge having a writing end and an exposed ink opening, wherein the writing end moves from a retracted position to an extended position for writing. The retractable ink pen includes a cap including a recess with an inner surface having one of: i) a position structure, and ii) both a first locator and a second locator spaced a distance from the first locator along a first longitudinal axis. The retractable ink pen further includes an elongate barrel including an outer surface having the other of the position structure and both the first locator and the second locator, wherein the position structure is located at the first locator when the writing end is in the retracted position and wherein the locating structure is located at the second locator when the writing end is in the extended position.

The adaptation of a pocket-size pen for use by a person is provided. The pen includes a cap with internally configured male threads, and a body. The body includes a barrel with externally configured and spaced apart first set of female threads, and second set of female threads. The barrel is hollow inside with a top opening for receiving a full-sized standard ink source. The male threads of the cap engage the second set of female threads of the pen body for closing a writing tip and reducing the length of the pen for storage in the pocket of a user. The male threads of the cap engage the first set of female threads of the body for transforming the pen into an extended-length pen similar in length to a conventional pen and revealing the writing tip for comfortable writing using the pen.