Screw and method to identify the screw

摘要

A screw has a head whose underside has impressions or embossings and faces towards the tip. The underside is divided into at least five sectors of the same size. Three-fifths of the sectors exhibit an identical pattern of impressions or embossings and at least one sector is provided with a different pattern of impressions or embossings or else with no impressions or embossings.