Knife

A knife kit comprising:

• a longitudinally elongated housing;
• a blade;
• a blade holder holding the blade and movable longitudinally between a safety position in which the blade is inaccessible within the housing and a cutting position in which the blade projects longitudinally at least partially out of the housing and in which a stop surface fixed relative to the housing engages a counterpart surface fixed on the blade holder;
• a spring connected between the blade holder and the housing and urging the blade holder into the safety position;
• a set of at least two interchangeable modules each having a retaining surface and a fastening formation, a spacing of the retaining surface of each module relative to the respective fastening formation being different from a spacing of the retaining surface of any other module from the respective fastening formation;
• a seat on the housing or on the blade holder fittable with any one of the modules but not more than one of the modules at the same time;
• and
• fastening means for fixing any single one of the modules but not more than one of the modules at the same time to the seat, the retaining surface of each module forming the stop surface when fixed in the seat of the housing or forming the counterpart surface when fixed in the seat of the blade holder, a longitudinal projection of the blade from the housing in the cutting position being defined by the longitudinal spacing of the retaining surface relative to the fastening formation of the module in the seat, the longitudinal spacings of the retaining surfaces from the respective retaining formations on the modules being different and defining different longitudinal projections of the blade from the housing depending on which module is in the seat.