Fasteners normal size metric thread in accordance with the differences in diameter and pitch into coarse and fine rib rib. Because there are a variety of different fastener size, accuracy, strength and manufacturing data, these elements combine to make countless varieties of fasteners thousands, many millions. Ontario said fastener products can be divided into yin yang rib rib class products and nut bolts class. In accordance with the head of the fastener to move parts of the shape have Phillips head, single slot head, hexagon-level. In addition, to deal with differences in utilization and usefulness, and another additional feature of the fastener, so fasteners classification is quite large.