Many enterprises do not know the actual specifications of screw when they use twill nut. Sometimes some newly developed products need new screw. A common self-tapping screw is the type of pointed tail: M4x10x18T PA, the general screw factory has seen that M4 refers to the diameter of the screw teeth, 10 refers to the length of the screw regardless of the head. (The expression length of the general screw does not count the head thickness, except for the countersunk F head and semi-countersunk O head) 18T refers to the number of teeth of the screw, but does not refer to the screw. There are 18 Yashan, but refers to 18 Yashan in an inch, 25.4MM in an inch, which is almost the same in the world. When the length of the screw is 10, there should be 7 Yashan (25.4_18x10).

Different sharpness has different uses. Of course, with the reduction of the diameter and length of the nail body, the degree of the tail will increase. For example, a self-attack of 1.7x10 can use 42 degrees, but a self-attack of 1.7x4 will use 45-50 degrees. Of course, most of the machine tooth screw is made of machine. Unlike self-tapping, self-tapping can be used on any surface. As long as the self-tapping force and hardness are strong enough, it can theoretically attack any object by itself. Mechanical screw has its limits in use. When using it, the mechanical screw must be pre-tapped on the object to be used. The expression method of the mechanical screw follows the self-tapping difference very little. For example, M4X10X0.7 is the outer diameter of 4mm plus the pitch of 0.7, that is, every 0.7mm has a pitch of 60 degrees. Of course, 10 is the effective length of the screw regardless of the head. Of course, M4 also has 0.5 young teeth. It is necessary for M4 to have a shorter effective strength. In general, the mechanical threads made in China are made in metric system, and there are 55 degrees made in Wyeth in British system. They have 47.5 degrees of BA teeth in electrical appliances. UNC and UNF threads are most easily confused with British teeth. Therefore, when making and customizing screws, the first thing to do is to find out what specifications of threaded teeth are. Distance, of course, is best if everyone has a multi-specification dental card. The chance of making a mistake is greatly reduced.

The screw is a tool to tighten the machine parts step by step by using the physical and mathematical principles of the oblique circular rotation and friction of the object. Screw is a general term for fasteners, which is spoken daily. Screws are indispensable industrial necessities in daily life: minimal screws used in cameras, glasses, clocks and watches, electronics, general screws used in TV, electrical products, musical instruments and furniture, large screws and nuts used in engineering, construction and bridges, and transportation equipment, aircraft, trams, automobiles, etc. Use both large and small screws. The screw has an important task in industry. As long as there is industry on the earth, the function of the screw will always be important. Screw is a common invention in people's production and life for thousands of years. According to the application field, it is the first invention of human beings.

Screw, also known as "Screw", "Screw" (screw), "screw" (screw). In fact, screw is a generic term, and screw, screw are different from each other. The screw is generally called wood screw; it is the kind with a sharp head at the front, with a large pitch, and is generally used to fasten wood and plastic parts. Screw is machine screw (mechanical screw), is the kind of front flat head, pitch is small, uniform, generally used to fasten metal, machine parts.

The first person to describe a spiral was the Greek scientist Archimedes (287 BC-212 BC). Archimedes spiral is a huge spiral in a wooden cylinder, used to raise water from one level to another and to irrigate fields. The real inventor may not be Archimedes himself. Maybe he just describes something that already exists. It may have been designed by skilled craftsmen in ancient Egypt to irrigate the banks of the Nile.

In the Middle Ages, carpenters used nails or metal nails to connect furniture to wooden structures. In the 16th century, nail makers began to produce nails with spirals that could connect things more firmly. That's a small step from such a nail to a screw.

Around 1550 AD, the earliest metal nuts and bolts as fasteners appeared in Europe. They were made by hand on simple wooden lathes.

The screwdriver (chisel) appeared in London around 1780. Carpenters have found that screwing a screw with a screwdriver can fix things better than hammering it, especially when it comes to threaded screws.

In 1797, Mozley invented a precision screw lathe made of all metals in London. The next year, Wilkinson made a nut and bolt machine in the United States. Both machines can produce universal nuts and bolts. Screws were quite popular as fixtures because a cheap method of production had been found at that time.

In 1836, Henry M. Philips applied for a patent for the screw with cross groove head, which marked a significant progress in screw base technology. Unlike the traditional slotted head screw, the edge of the cross slotted head screw head of the cross slotted head screw. This design makes the screwdriver automatically centered and not easy to slip, so it is very popular. General purpose nuts and bolts can connect metal parts together, so by the 19th century, the wood used to build machinery houses had been replaced by metal bolts and nuts.