The invention relates to a molding element for a mold for a tire comprising a tread provided with a plurality of blocks. Each block comprises a contact surface intended to come into contact with a road surface during running. The molding element also comprises a molding surface for molding the contact surfaces of the blocks. The molding surface comprises a plurality of ribs intended to mold fine grooves in the blocks. These ribs have a height of between 0.005 and 1 mm, a width of between 0.01 mm and 0.3 mm and the pitch (P) of the ribs is between 0.1 and 2 mm. The molding surface comprises at least one rib-free measurement zone able to accept measurement means. This measurement zone has the overall shape of a disc the diameter of which is greater than 3 mm.