What is a screw? It is commonly known as fastening piec […]
What is a screw? It is commonly known as fastening piece in spoken language. The screw is the essential industrial thing in the daily life. For example, the small-size screw is widely used in the camera, eyeglasses, clock and electron. As for the common screw, it is applicable for the television, electrical product, musical instrument and furniture. The large-size screw is commonly used in the construction project and bridge. The small-size one and large-size one are very suitable for the airplane, automobile and electric car. In a word, the screw has the important task on the industry. As long as there is industry in the world, the important role of the screw can not be overlooked.
Different standards, different categories. Besides for the small-size, large-size or middle-size, there are still different kinds of screws, which are often used in the industry according to different requirements, such as machine one, tapping one, sheet metal tapping one, wooden one and drywall one.
As for the material used in the screw, at present there is carbon steel, stainless steel and copper in the market. But not all carbon steel materials are widely used in the screw. Only the low carbon steel, medium carbon steel and alloy steel are commonly seen in the screw material. Because of the good heat resistance, corrosion resistance and welding capacity the stainless steel is quite popular in the screw industry. As for the copper, the standard screw adopts the brass, bronze and UNS C11000 Copper as the material.
Besides for the introduction about the categories and material, the specification of the screw will be briefly introduced in the following content. There are three common specifications for the screw, namely metric system, American standard and British standard. The unit for the metric screw is millimeter and its cusp angle is about sixties degrees. The unit for the American standard and British standard is inch. Their cusp angles are separately sixties degrees and fifty-five degrees. Owing to the different measuring units the ways to indicate the specification of the screw are different. For example, M16-2X60 shows the metric screw thread. Its meaning is that the nominal diameter of the screw is sixteen millimeters, pitch two millimeters and length sixty millimeters. Another example is 1/4-20X3/4, which indicates the British standard screw thread. Its meaning is that the screw has the one fourth inch nominal diameter and there are twenty pitches every inch. Besides, its length is three fourth inch. If people want to indicate the American standard screw, the following words "UNC" or "UNF" will be added in the back of the British standard one. Thus the way can distinguish the unified national coarse one and the unified national fine one.