Stainless steel as such has along history. The non-corrosive object came to existence from India. India has an art-craft called the Iron pillar of Delhi, which has a high-phosphorous-content in the Iron Pillar. Stainless steel which is now used came into existence in the early part of the 20th Century. In the beginning stainless steels fastener were made of 10-18% chromium, along with significant amounts of carbon. Now manufacturers have made stainless steel fasteners became a very widespread and the cost has been reduced.

The industry follows two major metric standards. One is DIN Detaches Institut für Normung (German) and the other is JIS Japanese Industrial Standards.  Not doubt these standards are closely related and most of the time identical yet the bolts of the same number can’t be identical. Some difference does exist. 

The screws length is measured from the bottom of the head. The length generally is given after the "x". In the case of a flathead screw, the designed is sitting in the flush of a countersunk material and is measured to the top of the head. 

In the case of unified threads the length is measured in inches. A 1/4-20 x 3/4 screw is .75 inches long. Sometimes the length is measured in fractional inches or the fractional equivalent. Where the metric threads are concerned the length is measured in millimeters. 

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