It is a metal piece, whose function is to join two or more elements, this type of bolt has a hexagonal head, made of carbon steel, quenched and tempered, high resistance for use in the mechanical and automotive industry, its resistance of load is similar to those of the grade 5 screw, it is identified by the number that it has in the upper part of the hexagon. The finish of the screws can be black or zinc plated with different thread pitches, bearing in mind that when mentioning a 931 screw we mean that it is a partial thread.