Screws are a very common thing in our life, and they are easily overlooked by people. When we need to use a small screw, we often do not know how to choose the correct screw. I would like to share some of my personal insights with you.
1, the size unit of the screwIn the world we have two very commonly used units of measure,The first is the metric unit, we usually use millimeters to mark the size of the screw
- Metric measurement: (decimal system)
1m=100cm=1000mmThe second is the imperial unit, usually expressed in inches to express the size of the screw
2. inch measurement: (8 system)
1 inch = 8 cents 1 inch = 25.4 mm 3/8,,×25.4 =9.523, 1/4,, The following products use the number to indicate their name diameter, such as:4#, 5#, 6#, 7#, 8#, 10#, 12# threadDifferent countries and regions will use different units, such as Germany, China usually use the metric unit millimeter to describe the size of the screw. The standards they use are also very close.The United States, the United Kingdom and other countries will use imperial units.So you have to know which size I need before choosing screws.
2, the function of the screw.The functions of screws are so many that it is impossible to describe them all in words.Here I can only introduce some commonly used functions.The main function of screws is to connect different parts together.For example, a self tapping screw uses its own thread structure to tightly connect the two parts together with the shape of the head by extruding the thread shape suitable for it.
Machine screws are used to connect the two parts with a standard thread and a pre-set standard internal thread on the connecting part or with a nut.
3, the shape of the screw
The shape of the screw can be described as all kinds of strange, people will use different shapes of screws according to their needs. Here we list some common standard screw shapesa,
A, The head shape of the screw
Pan head screws
Countersunk head screws
Cylinder head screwbutton head screw
B, the driving method of the screw
4, the material of the screw
There are many kinds of screw materials, including almost all kinds of common materials, such as: carbon steel, stainless steel, copper, nylon, iron, alloy, aluminum and so on.Among them, the most commonly used materials are carbon steel, and stainless steel. Carbon steel is relatively cheap, but its corrosion resistance is poor, the price is relatively cheap, and its application range is the most extensive; while stainless steel has better corrosion resistance and durable products. durable.
5, the performance level of the screw
The performance grades of bolts for steel structure connection are divided into more than 10 grades such as 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, 12.9, etc. Among them, the bolts of grade 8.8 and above are made of low-carbon alloy steel or medium-carbon steel and are heat-treated (quenching, tempering), commonly known as high-strength bolts, the rest are commonly known as ordinary bolts. The bolt performance grade label consists of two parts of numbers, which represent the nominal tensile strength value and yield ratio of the bolt material respectively.
Another: stainless steel bolts are usually marked as A4-70, A2-70,The difference between stainless steel screw A2-70 and A4-70 is to remove the “-70” at the back and leave it behind: A2 stainless steel and A4 stainless steel, A2 is 304 stainless steelQuality, A4 is 316 stainless steel, the main difference between the two is here, the latter “70” refers to the stainless steel tensile strength performance grade.