Author Guy Avellon's profile:
This article is taken from the May/June 2011 issue of the American Fastener Journal. Author Guy Avellon has been working in the repair industry for 30 years. He has served as manager of engineering management, product marketing and quality systems. Before engaging in the fastener industry, he was actively involved in metal coating work. Since 1988, he has been a member of SAE and a vice chairman of the ASTM Fasteners Committee, and concurrently chairman of the Fastener Test Method Committee. In 2005, Gay received the Merit Award from ASTM. A few years ago, he opened a GT technical consulting company to conduct fastener training and failure analysis for various industries, as well as conduct an ISO system audit and prepare operational instructions. Contact Guy Avery can send an email to Guy. or visit http://
Although the United States is the last country to use metrics, we have been using metrics for decades in pharmaceuticals, photography, the chemical industry, optics and even spark plugs.
When used as a length measurement unit, each metric size is based on meters, and the value is raised and lowered by moving the decimal point to the right to the left.
Therefore, if one meter is 1.00, one tenth of a meter is decimeter (dm) is 0.1m, one centimeter (cm) is one meter and one hundredth is 0.01m, one millimeter (mm) or one One thousandth of a meter is 0.001m. So, 1000mm=
100cm = 1m. These numbers remain the same, except that the decimal point moves. Going bigger, the next unit is 1000, which is expressed as 1 km (Km) or 1000 m.
We found an interesting phenomenon in metric units: all units of weight, length and volume are interconnected. A cube with a side length of 10 cm and a volume of 1,000 cubic centimeters. If the cube is filled with water, it has a volume of 1 liter (1 liter or 1000 milliliters) and weighs 1,000 grams or 1 kilogram.
Metric standard
A few decades ago, France, Italy, Germany, the United Kingdom, and Japan still did not have a standard agreement on metric fasteners. Although DIN (German Industrial Standards) has established standards that are better than any country, there is still a need for uniformity. ISO (International Organization for Standardization) was born.
The DIN standard was subsequently modified in accordance with the recommendations of the ISO. The United States has coordinated with ISO through the efforts of ANSI (American National Standards Institute). However, there are still some subtle differences.
Fastener marking
First, when ordering or identifying metric fastener sizes, we can identify them by the capital letter "M" in front of the metric fasteners, as all metric fasteners are preceded by the capital letter "M". Next, similar to the marking of the series of fasteners, the diameter, pitch, length and performance level are listed together, for example: M12 x 1.5 X 50, 10.9 hex head screws.
From this we can know that the hex head screw has a diameter of 12 mm, a pitch of 1.5 mm, a length of 50 mm and a performance rating of 10.9.
Pitch
Users must know that there are three types of pitch: the first, standard thread, similar to UNC; the second, fine thread, similar to UNF; the third, Japanese thread, is an interval value, and only applies to diameter M10 and M12 fasteners. For example, fasteners of diameter M10 have pitches of 1.0 mm, 1.25 mm and 1.50 mm.
The logo is especially important because many metric sizes are very close to the inch series. Nuts or fasteners may be mated at the beginning, but further tightening may result in a threaded snap. For example, a 1/4" 28 fastener has a diameter of 0.250", which is 0.014" compared to M6 measured at 0.236". The pitch of the M6 ​​is 1.0, which is approximately equal to 25.6 TPI per inch of thread, while the inch fastener is 28 TPI. Although there are not many differences, it is easy to cause confusion.
Table 1 lists other examples of the potential hazards of mixing and fitting metric and metric fasteners. The result of the mixing is that the resulting clamping force will be 25%-60% less than expected, in which case the load will be lost 100% regardless of whether the thread has no slip or start slip.Table 1.Inch thread and metric threadInch boltMetric nut10-32M5x0.81/4''-28M7x1.05/16''-18M8x1.03/8''-16M10x1.57/16''-14M12x1.751/2''-13M14x23/4''-10M20x2.53/4''-16M20x1.5Â Metric bolt inch nutM12x1.251/2''-20M18x2.53/4''-10M18x1.53/4''-16M24x31''-8M24x21''-12
Performance level
The strength of metric fasteners is called "Property Class" rather than "Grade". Nonetheless, the performance rating is roughly equivalent to the SAE rating system (see Table 2).Table 2. Metric gradePerformance levelSAE rating4.6Grade 14.8Grade 14.8Level 28.8Level 59.89% stronger than level 510.9Level 811.9no12.9ASTM A574
The easiest way to determine the performance rating of a fastener is by looking at the digital markings on the fasteners. These numbers with a decimal point are marked on the hex head or on the top or side of the grooving head fastener.
The bolt has a decimal point mark and the nut does not. For example, a nut that mates with a 10.9-level bolt will be marked 10 instead of 10.9.
The US automotive industry has developed Class 9.8 because some specifications of Class 8.8 fasteners do not provide the equivalent of SAE Class 5. This combines the stress distribution of the fastener strength with the head geometry.
The 8.8 performance rating mark is one of the most confusing areas. Many users confuse it with SAE Level 8. The difference in tensile strength between 120 ksi (828 MPa) and 150 ksi (1035 MPa) may have catastrophic consequences for critical applications.
Another issue that needs to be closely watched is the proper marking of the hex head cap screws. For American groove head products, only one strength grade of 1/2'' or less is 180ksi (1242MPa), which is also greater than 1/2'' specification, which is 170ksi (1173MPa). The metric groove head products are different and have three performance levels: 8.8, 10.9 and 12.9. When repairing European machinery, pay special attention to this and replace it with the same type of grooved product of the same strength designed by the factory.
The thread length requirements of DIN 931 and DIN 960 are essentially the same as ISO; for fasteners up to 125 mm in length, the thread length is 2 diameters plus 6 mm. For DIN 933 and DIN 961, the fasteners are fully threaded to the head, so the thread length is not mentioned.
Wrench size
Many mechanics complain that to tighten the same size fasteners, use two wrenches to tighten the bolt head and nut. Fortunately, this only happens in a few specifications. Due to the fundamental differences between DIN and ISO, the DIN fasteners of M10, M12 and M14 have a width of opposite sides (WAF) that is 1 mm wider than ISO, but the M22 DIN fasteners are 2 mm smaller than ISO.
Both types can be used and sold in the United States. It depends on what specifications the manufacturer uses and who will distribute them. If a company purchases from several dealers, then in the same storage cabinet, the nuts and bolt heads of different sizes may be purchased (see Table 3).Metric torqueTable 3. Metric wrench dimensionsNutDIN934ISOM1017mm16mmM1219mm18mmM1422mm21mmM2232mm34mm
The metric torque is expressed in Newton-meter (Nm). Physically, the unit of Newton's expression is commonly used. It is named after scientist Isaac Newton. A Newton equals 0.2248 pounds of force. We shifted the decimal point to the right by three places and got a thousand Newtons (KN) of 224.81 pounds.
Fastener strength
In this article, we learned what different performance level markers are, but what do they do? The term unit of strength used in metric is not "pounds per square inch" (psi) but Pascal. Because these units are large in value, the word "mega" is added to the front to become "megapascal" or MPa.
It is also interesting to note that the performance level number is actually related to the strength of the fastener. For example, the strength of the 8.8 grade fastener is 830 MPa, and the grade of 10.9 is 1040 MPa. The number of the metric mark is actually the tensile strength of the fastener in megapascals.
It should also be noted that although the "8" nut on the market can still be used with 8.8 grade fasteners, ASTM A563M only recognizes that the performance grade 9 nut can be used with 8.8 and 9.8 grade fasteners. Of course, its minimum guaranteed load stress is 900 MPa.
Table 4 lists the recommended torque values ​​for tightening the nut on the bolt threads.
The unit marked with * is inch-pound.Table 4. Recommended Torque Values ​​for Metric Fasteners (feet- pounds)Level 8.8Class 9.910.9 level12.9 levelGroove headAnd crossSlot headspecificationPitchdrylubricatingdrylubricatingdrylubricatingdrylubricatingM40.728*17*30*18*39*twenty four*53*33*4M50.857*34*61*37*78-*47*95M61.00859611715914M71.0014816102012M81.252012281737twenty two35M81.00twenty one13twenty one153018M101.5040twenty four5533734469M101.25412542255735M121.756942955712776120M121.257345754510563M142.001096515090203122M141.50116701157016095M162.00166100235140316190307M161.50175105180110245145M182.50225135325195M181.50250150355215M202.50325195455275615370580M201.50355215350210495300M222.50440265615370M221.50470280660400M243.0056033578047010666401000M242.00600360600360850510M273.008255001160700M303.50111567512007201580950219012711986M333.50152090021501290M364.001950117527501650M394.001550152535502130
The lubrication value is a metal lubricant such as anti-seize grease such as nickel or copper.
Translator's postscript
In the two consecutive editions of the American Fastener Journal, veterans of fasteners talked about their own views on metric fasteners, indicating the increasing exchange of fasteners in different fields.
In the magazine's March/April 2011 issue, Chris wrote the article "Metal Fasteners", which is mixed. In China, the experience of metric fasteners is not the case. In the market, on the Golden Spider Consulting Network, and in the forums of many fasteners, the people who use fasteners are not like the archaeologists, eagerly looking for the already revoked, revoked or It is a fastener standard that has expired, as well as various hardware manuals and various fasteners. They still remember these old standards, not for anything else, only for the needs of the market. Why is the market needed? Because even the young engineers, the mechanical design manual held in the hand is still the old standard; because many foreign-funded enterprises get Chinese mechanical projects, most of which are outdated goods, the old standard fasteners are still needed; because many machinery industry succeeds No one, but had to use the old drawings of the 50s and 60s...
How can this all of this not produce such a demand? Therefore, it is hoped that manufacturers and sellers of fasteners will be able to recommend new standards to customers in the future, reflecting the practical experience and technological progress of the fastener industry.
This article written by Guyi is also very interesting. The inch user sees the metric system, which is similar to how our metric user looks at the inch system. This may indicate the transition of the future system to the metric system. The values ​​in Table 4 are in pounds or pounds. To be converted into our familiar cattle, multiply by 1.356 and 0.113 respectively. Table 4 defaults to a hexagonal head. For a grooved head or a cross recessed head, look at the last column.
Author Guy Avellon, Golden Spider Fastener Network Consultant Wang Weiwu Translated Golden Spider "Fasteners" Quarterly Editorial Department
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