Adjustment ring which enables more precise adjustments compared with previous models, in order to match the particle size of the ground coffee to the humidity of the atmosphere, to the coffee blend and to the type of grinder. Aesthetically the new ring enables the control settings to be read more easily through intuitive labelling which indicates the correct direction with an arrow to regulate the grinding particle sizes. Technically, the new system allows for the distance between the burrs to be adjusted with an accuracy of one hundredth of a millimetre, thus enabling a more efficient extraction of the volatile elements and in turn obtain coffee with a superior aromatic character.