The writing instrument has a tubular body (12), guide shell (14), outer shell (32) and clip. The outer shell has at least one groove (32a) in its interior surface. The guide shell has at least one corresponding bead (14e) to act with the groove. A surface at an angle to the axial direction of the outer shell is made on the rear sector of each side wall of the groove so that it increases towards the rear end. The bead has a corresponding surface.
