Abstract: The measuring head intended for measuring diameters of cylindrical parts, e.g. parts being ground to diameter, comprises two measuring projections which are easily adjustable when a change is made from one diameter to another diameter, while maintaining excellent precision whatever the diameter concerned and the distance which separates the measuring head from the part to be machined. For this purpose, each of the measuring projections is a crank comprising a pivoted arm and a cylindrical rod projecting from the arm and forming a measuring contact element. The cranks are secured to an upper block and a lower block, respectively. A pick-up measures the distance existing between the blocks. The cranks are implemented in such manner that the axes of the rods always remain parallel to each other whatever the angle of rotation or adjustment of each of the arms.