Rancilio Rocky / MD40 / Obel Bregant 50mm espresso grinder burr set. 50mm OD X 31mm ID X 8 - SX (left hand/counter clock-wise) rotation. These are an O.E.M. product from Rancilio. For Rocky users: the burr mounting screws reportedly get VERY tight and may strip when you try to remove them. You may want to consider purchasing an extra set of six, part number MR_25