Damp telescopic tube and a damp writing pen

A damp writing pen, comprising a pen head, a pen cap, and at least two metallic tubes in different diameters which are a small tube and a big tube, the small tube being fitted in the big tube, a limit mechanism being provided between the small tube and the big tube, the small tube having a first end inserted in the big tube, the first end of the small tube being provided with a piston to be in touch with an inner wall of the big tube,

• wherein the piston comprises a piston shaft, including
• a short shaft at a smaller diameter end thereof, with the short shat being inserted and secured to the small tube;
• and
• a plurality of flanges spaced with each other at a larger diameter end thereof;
• and
• at least a piston ring, the piston ring is fitted on one end of the piston shaft, the piston ring has an outer surface to be in touch with the inner wall of the big tube, the piston shaft has another end inserted in and secured to the first end of the small tube, and an exhaust notch is formed in one of two ways:
• i) the exhaust notch is formed axially on each of at least two flanges at the larger diameter end of the piston shaft;
• or
• ii) the exhaust notch is formed on each of the one or more piston ring, not being completely covered by the piston ring upon which the exhaust notch is formed.