Writing instruments

An ink writing instrument comprising a body extending along an axis, the body having a first end and a second end opposed to the first end along the axis, the first end being provided with a writing tip and with an eraser, wherein the writing tip is configured to be fed with ink and the eraser is movable along the axis with regard to the body, the ink writing instrument further comprising a helical-cam propelling mechanism configured to move the eraser along the axis between a retracted position and a protruded position, and the helical-cam propelling mechanism comprising a helical cam radially protruding from one of the eraser and the body, and two cam followers arranged on the other of the eraser and the body, the two cam followers axially sandwiching the helical cam at least when the eraser is moved between the retracted position and the protruded position, wherein the first end is provided with a protective cover that is fixed with respect to the body, wherein the protective cover has at least one cut, and wherein the protective cover is configured to be elastically deformed from a rest configuration to a deformed configuration so as to allow passage of the eraser through the at least one cut when the eraser is moved from the retracted position to the protruded position and to return to a rest configuration when the eraser is moved from the protruded position to the retracted position.