Steering tool with controlled distal flexibility

A steering tool comprising:

• an internal tube disposed inside an external tube, proximal ends of said internal and external tubes being arranged for longitudinal axial movement relative to one another, wherein a distal end of said internal tube is fixedly joined to a distal end of said external tube;
• a tube manipulator operative to cause relative axial movement of said proximal ends of said internal and external tubes and bending of a distal portion of at least one of said internal and external tubes;
• a control knob connected to a stopper which is movable by said control knob towards or away from an abutment element mounted on at least one of said tubes, and wherein said control knob is selectively lockable at a plurality of locked positions;
• and
• a biasing device positioned between said stopper and said abutment element and configured to apply a variable biasing force on said abutment element, wherein a magnitude of said variable biasing force is determined by a position of said stopper, the position of said stopper being determined by which of said plurality of locked positions said control knob is locked thereat, and
• wherein in a first position of said locked positions of said control knob, said biasing device is at a fully biased position in which it applies a sufficiently strong biasing force on said abutment element to completely inhibit movement of said proximal ends of said internal and external tubes relative to one another, and in a second position of said locked positions of said control knob, said biasing device is at a partially biased position in which it applies a relatively weak biasing force on said abutment element to partially inhibit movement of said proximal ends of said internal and external tubes relative to one another.