A surgical implement for orientating a tool at a predetermined angle with respect to a plane of a target surface to be engaged by the tool, said implement comprising: a rod having a longitudinal axis, a proximal end, and a distal end; a tube enclosing said rod, and having a proximal end at the proximal end of the rod; and a head coupled to the distal end of said rod; said head at said distal head of said rod being formed with three contact points arranged in a circular array around said longitudinal axis; wherein said predetermined angle is 90°, such that the longitudinal axis of said rod is perpendicular to said plane of said target surface when said three contact points are in contact with said plane of said target surface;wherein said tube has a larger diameter than said rod such that when said three contact points are in contact with said target surface, and said tube is manipulated such that the proximal end of the rod is centrally of the proximal end of the tube, said tube is oriented at said predetermined angle with respect to said plane of the target surface; characterised in that said contact points are formed in three elastically deformable segmental elements (24A-24C) that are defined by three axially extending slits (25A-25C)formed in the distal end of said head, said slits intersecting at said longitudinal axis of said rod; said segmental elements being radially displaceable from inner positions to outer positions with respect to each other and to said longitudinal axis such, that when in their outer positions and in contact with the target surface, the three contact points define a plane on the target surface at said predetermined angle to said longitudinal axis of the rod; and in that in said inner position of said segmental elements removal of said rod and head from said tube through the proximal end of the tube is permitted. a rod having a longitudinal axis, a proximal end, and a distal end; a tube enclosing said rod, and having a proximal end at the proximal end of the rod; and a head coupled to the distal end of said rod; said head at said distal head of said rod being formed with three contact points arranged in a circular array around said longitudinal axis; wherein said predetermined angle is 90°, such that the longitudinal axis of said rod is perpendicular to said plane of said target surface when said three contact points are in contact with said plane of said target surface;wherein said tube has a larger diameter than said rod such that when said three contact points are in contact with said target surface, and said tube is manipulated such that the proximal end of the rod is centrally of the proximal end of the tube, said tube is oriented at said predetermined angle with respect to said plane of the target surface; characterised in that said contact points are formed in three elastically deformable segmental elements (24A-24C) that are defined by three axially extending slits (25A-25C)formed in the distal end of said head, said slits intersecting at said longitudinal axis of said rod; said segmental elements being radially displaceable from inner positions to outer positions with respect to each other and to said longitudinal axis such, that when in their outer positions and in contact with the target surface, the three contact points define a plane on the target surface at said predetermined angle to said longitudinal axis of the rod; and in that in said inner position of said segmental elements removal of said rod and head from said tube through the proximal end of the tube is permitted.