Abstract: Tool (10) with diamonds (35) (35') (36) for dressing grinders (90) having a roller (11) rotating on a supporting shank (20) round an axis that intersects the axis of the shank (20) at an angle of 45.degree., with operative areas (30) (31) having one or more diamonds (35) (35') (36) placed at equal angular distances or continuously over a conical geometrical surface (16) with a taper of 90.degree. so as to be intersected by the geometrical plane passing along the axis of rotation and the axis of the shank according to a straight line orthogonal to the latter. Ref. FIGS. 1 and 3.