GB/T 3098.2-2000 Mechanical properties of fasteners - Coarse thread nuts
Some standard content:
National Standard of the People's Republic of China
Mechanical properties of fasteners - Nuts -- Coarse thread
Mechanical properties of fasteners - Nuts -- Coarse threadGB/T3098.2—2000
Approved and issued by: State Administration of Quality and Technical SupervisionDate of issuance: September 26, 2000
Effective date: February 1, 2001
14—6—1
This standard is equivalent to the international standard ISO898-2:1992 "Mechanical properties of fasteners Part 2: Coarse thread of nuts with specified proof load values":
GB/T3098 is generally titled "Mechanical properties of fasteners" and includes the following parts:
---GB/T 3098.1--2000
Bolts, screws and studs
-GB/T 3098.2—2000
Coarse pitch thread
-GB/T 3098.3—2000
Set screw
----GB/T 3098.4--2000
Female fine pitch thread
-GB/T 3098 . 5--2000
Tapping screw
-GB/T 3098.6--2000
Stainless steel bolts, screws and studs
Mechanical properties of fasteners
Mechanical properties of fasteners
Mechanical properties of fasteners
Mechanical properties of fasteners
Mechanical properties of fasteners
Mechanical properties of fasteners
Mechanical properties of fasteners
)Mechanical properties of fasteners
--GB/T 3098.7—2000
Extruded screws
-GB/T 3098.8--1992
Mechanical properties of fasteners
Thermal threaded connection pairs
-GB/T 3098.9--1993
Effective rectangular steel hexagonal lock nuts
-GB/T 3098.10—1993
Mechanical properties of fasteners
Mechanical properties of fasteners
Bolts, screws, studs and nuts made of non-ferrous metals GB/T 3098.11—1995
Self-drilling and tapping screws
-GB/T 3098.12—1996
Nut cone proof load test
GB/T 3098.13—1996
Mechanical properties of fasteners
Mechanical properties of fasteners
Mechanical properties of fasteners
Torque test and breaking torque of bolts and screws, nominal diameter 1～
-GB/T 3098.14—2000
Nut expansion test
--GR/T 3098.15-2000
Stainless steel nuts
-GB/T 3098.16—2000
Mechanical properties of fasteners
Mechanical properties of fasteners
Mechanical properties of fasteners
Stainless steel set screws
GB/T3098.17—2000 Mechanical properties of fasteners Hydrogen embrittlement inspection Preload test Parallel bearing surface method This standard adjusts the content of "scope" (ISO) 8982
1992 is not consistent with ISO898-6:1994), and is consistent with GB/T3098.4 (Chapter 1).
This standard does not adopt Appendix B of ISO898-2, and its content has been listed in the referenced standards in Chapter 2 of this standard. This standard is a revision of GB/T3098.2—1982, and the main modifications are as follows:
a) "Coarse pitch thread" is added to the standard name; b) Only mechanical properties tested under ambient temperature of 10~35℃ are specified. At higher or lower temperatures, its mechanical and physical properties may be different (Chapter 1);
c) "Minimum thread diameter" is cancelled in the scope of application (Chapter 1); d) "Nut" column is added to Table 2 and "It is feasible for the stress of the bolt-nut assembly to be higher than the yield strength of the bolt or the guaranteed stress" is added to the table notes;
e) Rockwell hardness value is deleted from Table 5, and the "heat treatment" state and "type" column of the nut are added, and the table notes are adjusted; f) Some guaranteed load values are adjusted (Table 6); g) The conversion table of Burk, Rockwell and Vickers hardness is added (Article 8.2); h) The test of surface defects is added (Article 8.3); i) For products that must be marked with performance grades, it is mandatory to mark the manufacturer's trademark or identification mark, which should be provided as much as possible as long as it is technically feasible. However, in any case, the packaging should be marked (Article 9.5). This standard replaces GB/T3098.2-1986 from the date of implementation.
Appendix A of this standard is a prompt appendix. This standard is proposed by the State Machinery Industry Bureau. This standard is under the jurisdiction of the National Technical Committee for Standardization of Fasteners. This standard is drafted by the Mechanical Science Research Institute, Xi'an Standard Parts Factory, Shanghai High Strength Bolt Factory, Shanghai Fastener and Welding Material Technology Research Institute, Beijing Standard Parts Industry Group Corporation, Wuhan Automotive Standard Parts Research Institute and Shanghai Jinma High Strength Fastener Co., Ltd., and the Secretariat of the National Technical Committee for Standardization of Fasteners is responsible for the interpretation of this standard.
ISO Trademark
ISO (International Organization for Standardization) is a worldwide federation of national standard bodies (ISO member bodies) of various countries. The development of international standards is usually carried out through ISO technical committees. Each member body can also participate in the committee if it is interested in the project carried out by a technical committee. International organizations, both governmental and non-governmental, related to ISO, can also participate in this work. ISO has close ties with the International Electrotechnical Commission (IEC) in the field of electrical standardization. Draft international standards adopted by technical committees are circulated to all member bodies for voting. The official publication of international standards requires at least 75% of the member bodies to vote in favor.
International Standard ISO898-6 was developed by ISO/TC2 Technical Committee for Fasteners SC1 Subcommittee on Mechanical Properties of Fasteners. The second edition has been amended and supplemented to the first edition (IS) 898-2:1980) and is a technical revision.
ISO898 is generally known as "Mechanical Properties of Fasteners" and includes the following parts:
-Part 1: Bolts, screws and studs
-Part 2: Nuts with coarse threads with specified guaranteed load values
-Part 5: Set screws and similar threaded fasteners not subject to tensile stress
-Part 6: Nuts with fine threads with specified guaranteed load values
Part 7: Torque test and minimum torque test for bolts and screws with nominal diameter 1-10mm
Appendix A and Appendix B of this standard are indicative appendices. 14—6-3
This standard specifies the mechanical properties of nuts with guaranteed load values when tested at an ambient temperature of 10~35℃. Products that are judged to comply with this standard under this ambient temperature condition may have different mechanical and physical properties at higher or lower temperatures, and users should pay attention to this.
This standard applies to nuts:
Nominal thread diameter D≤39mm;
Ordinary thread in accordance with GB/T192;
Combination of coarse thread diameter and pitch in accordance with GB/T 193;
Basic dimensions in accordance with GB/T196;
Tolerances and fits in accordance with GB/T197; Have specific mechanical requirements:
Width across flats in accordance with GB/T3104 or equivalent; Nominal height ≥0.5D;
Made of carbon steel or alloy steel.
This standard does not apply to nuts with special performance requirements, such as: locking performance (GB/T3098.9);
weldability;
corrosion resistance (GB/T3098.15);
performance requirements for working temperatures above +300℃ or below -50℃.
1. Nuts made of free-cutting steel cannot be used above +250℃. 2. For special products, such as nuts for high-strength bolts and hot-dip galvanized bolts in bolt structures, see the product standards for relevant values. 3. When the thread tolerance of the mating part is greater than 6H/6g, the risk of stripping will increase.
4.In the case of other tolerances or greater than 6H, a reduction in the tripping strength should be considered, see Table 1.
Referenced standards
Reduction of thread strength
Test load ratio, %
Thread tolerances
The provisions contained in the following standards constitute the provisions of this standard through reference in this standard. The versions shown are valid at the time of publication of this standard. All standards are subject to revision and parties using this standard should explore the possibility of using the latest version of the following standards. GB/T 41-2000
Hexagonal nut
4034:1999)
GB/T 192--1981
GB/T 193—1981
(diameter 1-600mm)
GB/T 196--1981
(1 ~600mm)
GR/T 197--1981
diameter 1 ~355mm)
GB/T 230-1991
GB/T 231--1984
Grade C (eqv ISO
Ordinary thread, basic tooth profile
Ordinary thread
Ordinary thread
Ordinary thread
Diameter and pitch series
Basic size (diameter
Tolerance and fit (straight
Metal Rockwell hardness test method
Metal Brinell hardness test method
GB/T 1800.2—1998 Limits and fits
Part: Basic provisions for tolerances, deviations and fits (eqvISO286-1:1988)
GB/T 3098.9--1993
Mechanical properties of fasteners
Rectangular steel hexagonal lock nuts (eqvISO2320:1983) GB/T3098.15-2000 Mechanical properties of fasteners Pot nuts (idt ISO 3506-2: 1997) Effective force
GB/T3104—1982 Width across flats of hexagonal fasteners (eqv ISO 272: 1982)
GB/T 4340.1—1999
Metallic Vickers hardness test
Part: Test method (eqv ISO6507-1: 1997) GB/T 5779.2—2000
(idt ISO 6157-2: 1995)
Fastener surface defects
GB/T5780—2000 Hexagon head bolts
4016: 1999)
GB/T 5781—2000
(eqv ISO 4018: 1999)
Hexagon head bolts
Grade C (eqv ISO
Full thread
GB/T 5782—2000
0Hexagon head bolts (eqvISO4014:
GB/T 5783—2000
ISO 4017: 1999)
GB/T 5784—1986
(eqv 4015: 1979)
GB/T 6170—2000
4032:1999)
Hexagon head bolt
Hexagon head bolt
Full thread (eqv
(eqvISO
Type 1 hexagon nut
GB/T 6172.1--2000
4035:1999)
GB/T 6174—2000
ISO 4036 : 1999)
GB/T 6175—2000
Hexagon thin nut
(eqyISO
Hexagon thin nut
Without chamfer (eqy
Type 2 hexagon nut (eqv ISO
4033:1999)
ISO4964:1994 Steel
Hardness conversion
3 Marking system
3.1 Nuts with nominal height ≥0.8D (effective thread length ≥0.6D)
Nuts with nominal height ≥0.8D (effective thread length ≥0.6D) are marked with the first part of the number of the bolt property grade mark; the bolt should be the one with the highest performance grade among the bolts that can match the nut (Table 2).
Marking system for nuts with nominal height ≥0.8D Matching bolts, screws and studs
Performance grade
Thread specification range
3.6, 4.6, 4.8
3.6, 4.6, 4.8
5.6, 5.8
≤M39
Thread specification range
≤M16
≤M39
≤M16
≤M39
Note: Generally speaking, nuts with higher performance grades can replace nuts with lower performance grades. It is feasible for the stress of the bolt-nut assembly to be higher than the service strength or proof stress of the bolt. Due to over-tightening, threaded assemblies may produce the following failure modes:
a) screw fracture;
b) screw thread stripping;
c) nut thread stripping;
d) nut and screw thread stripping.
The fracture of the screw occurs suddenly and is easier to find, while the stripping occurs gradually, which is difficult to find and increases the risk of accidents caused by fastener failure.
Therefore, for the design of threaded connections, it is always hoped that the failure mode is screw fracture. However, due to various factors (material strength of nuts and bolts, thread clearance and width across flats, etc.) that affect the stripping strength, this failure mode cannot be guaranteed in all cases. For M5M39 bolts, screws or studs, nuts with appropriate performance grades are selected according to Table 2. When tightened to the bolt (screw or stud) to ensure the load, the thread assembly will not have thread stripping.
However, tightening beyond the proof load of the bolt sometimes occurs, so the design of the nut should at least ensure that when the overtightening is 10%, the failure of the threaded assembly is the screw fracture, so as to warn the user that the assembly operation is improper.
Note: For more detailed information on the strength of threaded assemblies and nut types, see Appendix A (Indicative Appendix).
3.2 Nuts with nominal height ≥ 0.5D and < 0.8D (effective thread length ≥ 0.4D and < 0.6D)
Nuts with nominal height ≥ 0.5D and < 0.8D (effective thread length ≥ 0.4D and < 0.6D) are marked with two digits: the second digit represents 1/100 of the nominal proof stress measured with a rate hardness test mandrel (in N/mm2); and the first digit "0" indicates that the load-bearing capacity of this bolt-nut assembly is greater than that of a rate hardness test mandrel. The measured load-bearing capacity is smaller and also smaller than the load-bearing capacity of the bolt-nut assembly specified in Article 3.1. The effective load-bearing capacity depends not only on the hardness of the nut itself and the effective length of the thread, but also on the tensile strength of the matching bolt. Table 3 gives the marking system and guaranteed stress of nuts.
Table 3 Marking system and guaranteed stress of nuts with nominal height ≥0.5D and <0.8D
Nut performance grade
4Material
Nominal guaranteed stress
Actual Actual guaranteed stress
Table 4 specifies the materials applicable to each performance grade of nuts. The chemical composition of the materials shall comply with the provisions of the relevant material standards. Package 4
Performance grade
41), 51), 61)
Chemical composition, %
0.0600.150
0.250.060.150
0.0480.058
1) This performance grade can be made of free-cutting steel (unless otherwise agreed by the supply and demand parties) 2) To improve the mechanical properties of nuts, alloy elements may be added if necessary.
Nuts with performance grades 05, 8 (>M16 type 1 nuts), 10 and 12 should be annealed and tempered. 5 Mechanical properties
When tested according to the method specified in Chapter 8, the mechanical properties of nuts shall comply with the provisions of Table 5.
Surface defects shall comply with GB/T5779.2. 14-6-5
Thread specification
Vickers hardness
N/ninminmaxHeat treatment type
Thread specification
Thread specification
iN/mm2
Thread specification
M10JM16
188302
Vickers hardness
Mechanical properties
Non-fired thin type 500
Vickers Hardness
mininaxi Heat treatment type
Quenching and
272||353
minmax
Vickers hardness
Heat treatment
No quenching
minmax" Heat treatment
180302
No quenching
Vickers hardness
Vickers hardness
Vickers hardness
Vickers hardness| |tt||mnimax
Vickers hardness
max heat treatment|type
no quenching
Vickers hardness
minmax heat treatment
Heat treatment
Quenching and
no quenching
minmax
12331353
Vickers hardness
IN/mm2
Heat treatment
No quenching
Heat treatment
No quenching
Economic quenching and
Heat treatment
Quenching and
Vickers hardness
Heat treatment
Quenching and
Note: The hardness tester is mandatory for heat-treated nuts or nuts that are too large to be tested for the guaranteed load; it is not mandatory for other nuts, but is a guide. For nuts that are not quenched and tempered, but can meet the guaranteed load test, the minimum hardness should not be used as a basis for rejection. 14--6— 6
6 Guaranteed load
Table 6 specifies the guaranteed load values for coarse-pitch nuts. Among them, the stress cross-sectional area A of the thread is calculated as follows:
A=(+d)
Thread specification
Basic size of the middle diameter of the external thread, mm;
Basic size of the minor diameter of the external thread (d,) minus the lost screw to ensure
The stress
cross-sectional area of the thread
115100
1/6 of the original triangle height (H), that is:
Original triangle height of the thread (I
0.866025P), mm;| |tt||Pitch, mm;
Pi, yuan=3.1416
(A,×S,)N
Guaranteed load
101200
138200
100300| |tt||136900
109300|120800|134600
164900183700
149200
109900
170900 176600|203500
138200
176600
121000
176400 225400 218100225400 259700122500|125000 154400
0|218200278800|269700|278800321200
154500190900
151500
0324800|314200324800
176500 180000|222400
134100
254200
374200
0|229500|234100|289200| |tt||422300408500422300486500
330500
174400
213200|280500286100 353400403900516100 499300516100 594700
638500617700638500735600
263700 347000 353900 437200
01499700
416700 514700 588200 751600 727100751600 866000310500408500
370900 488000 497800|614900 702700 897900|868600 897900 1035000Failure load of nuts with nominal height ≥0.5D and <0.8D7
Table 7 gives the failure load values of bolts with different performance grades for guidance. For bolts with lower performance grades, the expected failure mode is bolt thread stripping, while for bolts with higher performance grades, the expected failure mode is nut thread stripping.
Nut performance grade
Minimum stress in the bolt when stripping
|Guaranteed load of nuts
Minimum stress in the bolt core when stripping, N/mm
Bolt performance grade
290370bZxz.net
8Test method
186800
230400
294000
363600
423600
550800
673200
832800
980400
1171000
Guaranteed load test
For nuts with specifications ≥M5, the guaranteed load is the arbitration method.
Install the nut on the hardened threaded mandrel as shown in Figures 1 and 2. During arbitration, the tensile test shall prevail. Apply a proof load along the axial direction of the nut and last for 15 seconds. The nut should be able to withstand the load without stripping or breaking. After unloading, the nut should be able to be screwed out by hand or loosened with the help of a wrench, but not more than half a turn. During the test, if the threaded mandrel is damaged, the test will be invalid.
The hardness of the threaded mandrel should be 45HRC
The thread tolerance of the threaded mandrel is 5h6g, but the major diameter should be controlled within a quarter of the lower limit of the 6g tolerance band. 14-6— 7
Ping hard
d,=d(D111))
Figure 1 Axial tensile test
1) D11 is in accordance with GB/T1800.2.
8.2 Hardness test
For routine inspection, the hardness of the nut should be tested on a support surface, and the average hardness of three points with an interval of 120° should be taken as the hardness value of the nut. In case of dispute, the hardness test should be carried out on the longitudinal section through the axis of the nut and as close to the major diameter of the thread as possible. The Vickers hardness test is an arbitration test and the test force of HV30 should be used.
When Brinell and Rockwell hardness tests are used, the conversion table given in ISO4964 should be used.
The Vickers hardness test shall be in accordance with GB/T4340.1. The Brinell hardness test shall be in accordance with GB/T 231. The Rockwell hardness test shall be in accordance with GB/T230.
8.3 Surface defect inspection
Performance level
Sign code
Selected sign
Sign symbol
(clock face method)
14—6—8
Hardened
d,=d(D1)
Figure 2 Axial compression test
1) D11 According to GB/T 1800.2. Surface defect inspection see GB/T5779.2.
9 Sign
9.1 Code
Sign code see Table 8 and Table 9.
9.2 Identification
Hexagonal nuts of all performance levels with thread specifications ≥M5 shall be marked with concave characters on the bearing surface or side of the nut, or with convex characters on the chamfered surface, or with a clockface marking method with concave characters on the bearing surface, as shown in Figures 3 and 4, in accordance with the marking system specified in Chapter 3. The convex character marking shall not exceed the bearing surface of the nut.
9.3 Marking of left-handed threads
Nuts with left-handed threads shall be marked with a concave arrow on one of the bearing surfaces as shown in Figure 5.
Nuts with thread diameter ≥5mm are required to be marked. The left-handed thread marking shown in Figure 6 may also be used. According to 3.1 Marking code for nuts with performance grades specified in Article 5
Optional
Performance grade
Marking code
Marking symbol
(clock face method)
1) The manufacturer's identification mark cannot be used instead of the dot. Table 9
Performance grade
Marking of nuts with performance grades specified in Article 3.2 04
Figure 3 Example of marking with code
Figure 5 Marking for left-hand thread
9.4 Selection of marking
The optional marking specified in Articles 9.1 to 9.3 shall be selected by the manufacturer.
9.5 Trademark (identification) mark
The dot may also be replaced by the manufacturer's identification mark
Figure 4 Example of marking with symbol (clock face method)Figure 6 Optional marking for left-hand thread
51) - Width across flats.
For products that must be marked with the property grade, the manufacturer's trademark or identification mark is mandatory and should be provided as far as technically feasible. However, in any case, the packaging should be marked. 14--6— 9
Appendix A
(Indicative annex)
Load-bearing capacity of bolted connections
(Notes on strength and design of nuts by ISO/TC2 Technical Committee on nuts)
Following the ISO recommendations for the adoption of property grades for bolts and screws (ISO/R898:1968), the ISO recommendations for the property grades for nuts (ISO/R898-2) were published in 1969. These ISO recommendations proposed a new system of marking and technical requirements for marking the property grades of bolts, screws and nuts, as well as a clear argument for the load-bearing capacity of a pair of bolt-nut assemblies.
a) The marking codes for bolts and screws indicate: minimum tensile strength and yield strength ratio.
For example: Performance grade 8.8
The first part number (the "8\" in 8.8) = 1/100 of the minimum tensile strength (N/mm2);
The second part number (the "8\" in 8.8) = 10 times the strength ratio (0.8).
The product of these two numbers (8×8=64) = 1/10 of the minimum yield stress (N/mm2).
b) The marking code of the nut indicates:
The marked number is equal to 1/100 of the minimum tensile strength (N/mm2) of the bolt or screw that matches the nut. When the bolt or screw matches the nut, the load it bears can reach the minimum yield stress. For example: 8.8 grade bolts or screws match 8 grade nuts: their load-bearing capacity can reach the minimum yield stress of the bolt or screw. With the release of ISO recommendations, this set of performance grade system has been widely promoted worldwide and has been proven to be successful in practice. In 1973, the SC1 subcommittee of ISO/TC2, on the basis of collecting practical experience, began to revise the ISO recommendations and planned to convert them into ISO standards. In 1974, the draft ISO/DIS 898-1 for the performance grades of bolts and screws was released. Among them, some modifications and additions were made, but the principle of the performance grade system was not changed. This draft was revised again, and the second revised draft was proposed in 1977 and accepted by the vast majority of ISO member groups. After the comprehensive revision of the draft on the performance grades of bolts and screws, a final resolution satisfactory to the relevant countries was formed in the SC1 subcommittee of ISO/TC2. Now ISO also agrees with this resolution. In the future, the essence of the technical requirements involving a wider range is to revise ISO Recommendation ISO/R 898-2 and convert it into an ISO standard for the performance grades of nuts. Experience has shown that the concept of specifying the performance grades of connecting parts with nuts with a nominal height of 0.8D is simple and clear, but it does cause some difficulties in practice. First, it is often difficult or impossible to achieve the specified nut performance using the most economical materials and processes, for example, fine pitch threads and coarse pitch threads of certain specifications. Even if the performance requirements are met, it is not necessarily guaranteed that the assembly will not be threaded during the tightening process. Previously, it was believed that the design requirements could be met if the proof load of the nut was equal to the minimum ultimate strength of the bolt. However, the emergence of the yield point tightening method and the new view of the interaction between the nut and the bolt thread requires the redesign of the nut to ensure better prevention of internal and external thread stripping. For example, the tensile strength of 8.8-grade bolts with thread specifications equal to or less than M16 is 800-965N/mm2 (the latter is determined by the maximum hardness), the yield strength ratio is 80%, and the yield strength is 640-772N/mm2. If the yield point tightening method is used, it is obvious that the tightening stress will be close to the proof stress. In addition, the latest research shows that the stripping strength obtained by testing nuts with hardened mandrels is higher than that obtained by testing nuts with bolts of the corresponding performance grade. For example, the test results of 8-grade nuts with a 45HRC mandrel are about 10% higher than those of 8.8-grade bolts with similar dimensions to the mandrel. Therefore, a nut with a proof load of exactly 800 N/mm2 measured with a hardened mandrel can be expected to withstand a stress of only about 720 N/mm2 when matched with a Class 8.8 bolt at the minimum practical size. If the tightening stress exceeds this value, thread stripping may occur. In particular, it is believed that the tensile strength of the bolt will also decrease by about 15% under the application of torsional loads, and the stripping strength of the assembly will also decrease by almost the same amount. Therefore, from the mechanical properties of the bolt, thread stripping may occur frequently when the service point tightening method is used for installation. In addition to the service point tightening method, the revision of some ISO standards is to consider reducing the tendency of thread stripping. Improve the mechanical properties of bolts and screws, as shown in Table AI (extracted from ISO898~1), so as to fully utilize the strength of common materials of Classes 4.8, 5.8, 8.8 (larger than M16), 10.9 and 12.9. In addition, in order to fully utilize the material, the width across flats of some hexagonal products is also considered to be reduced at this time. To take into account the impact of these changes and other factors, several member groups of ISO/TC2 SC1 (Canada, Germany, New Zealand, Sweden, the United Kingdom, the United States) conducted studies and extensive testing on bolt-nut assemblies. The tests included all product specifications, strength levels and materials. In general, the tests were carried out under typical fastener production processes and using standard materials. The test parts were accurately measured for size and material strength, and the data were then appropriately statistically analyzed. The results of the various researchers were compiled and summarized by Canada and found to be well interrelated. From this, a series of formulas were derived that can be used to predict the strength of assemblies that meet the basic tooth form of ISO 68 threads. These results were fully discussed within SC1 and in many national committees.
Initially, the committee ignored the resistance to changing the existing technical requirements, but the test results clearly showed that improved fastening methods and improved mechanical property levels alone could not prevent the assembly from stripping. The problem was that one of the threads of the bolt and the nut had stripped. As the results of the study showed, it was concluded that the most feasible way to solve this problem was to increase the height dimension of the 0.8D nut. This appendix is not intended to provide detailed instructions for guiding tests and methods for improving nut design. If necessary, the reader can refer to the 1997 SAE Journal No. 770420, EM Alexander, "Analysis and Design of Threaded Assemblies". For nuts of grades 4 to 6, according to Alexander's theory, the maximum hardness of the bolt given in ISO898-1 is not 250 HV (Table A1), because the maximum hardness only appears at the end or head of the bolt. Therefore, the calculation should be based on the actual maximum hardness of the screwed part of the bolt thread (Table A2).
Similar hardness values given by similar grades have been specified in ISO/R898-1:1968.
The above works show that there are many factors that affect the thread stripping strength. These include: accuracy, pitch, flare of the nut minor diameter, size of the chamfer inside the nut, strength matching of the nut and bolt threads, screwing length, width of the nut and similar (such as hexagonal flange surface), number of threads in the friction coefficient clamping, etc. On this basis, the analysis of fasteners of various specifications shows that: in the past, it is inappropriate to use a fixed nut nominal height (such as 0.8D), and it is better to design an appropriate stripping strength for each standard push assembly. The nut height given by this analysis is shown in Table A3.
It can be seen that there are two types of nuts, and type 2 is about 10% higher than type 1. Type 1 height is mainly suitable for performance levels 4, 5, 6, 8, 10 and 12 (up to M16), while type 2 dimensions are mainly suitable for performance levels 8, 9 and 12. Type 2 nuts mainly provide an economical cold-formed nut for 9.8 grade bolts and screws, and also for 12.Grade 9 bolts and screws provide heat-treated nuts with good toughness. The expected application range of the two types of nuts is shown in Table 5. As can be seen from Table 5, increasing the number of nut types does not mean doubling the number of nut varieties. There are only two cases of overlap between type 1 and type 2 nuts. For type 1: Grade 8 nuts less than or equal to M16 are allowed to be unquenched and tempered (cold formed, low carbon): Grade 8 nuts larger than M16 must be quenched and tempered. At this time, it is possible to use unquenched and tempered, thicker type 2 nuts instead of type 1 nuts, which is an economic issue of comprehensive analysis. For grade 12; the use of type 1 nuts with specifications larger than M16 is not appropriate. Due to the requirement to ensure the load, the hardness of the nut needs to be increased, resulting in a weakening of toughness. From a practical point of view, toughness is required. Therefore, in this case, thicker, quenched and tempered type 2 nuts are required. If necessary and possible, limit the use of nuts with specifications larger than M16, and there will be no overlap between type 1 and type 2 for grade 12 nuts. After the dimensions of the nuts have been determined according to the strength specifications of the assembly, the proof loads of these nuts are determined using hardened mandrels of defined thread size. As a result, the proof stresses of nuts of the same property class are not constants but vary with the specification. Table 5 gives the revised proof stress and hardness values. Hexagonal thin nuts with reduced load capacity for property classes 04 and 05 (formerly 06) are also given in Table 5: for these nuts, the design does not take into account the stripping strength but simply specifies a fixed height of 0.6D. Table 5 gives the proof stresses according to the standard tolerance 6H commonly used for mechanical fasteners. When used for larger tolerances or clearances, these stresses should be corrected by the factors given in Table 1.
Table 5 and Table 1 are only applicable to coarse pitch threads. For nuts with fine pitch threads, see ISO)898-6 (GB/T 3098.4). The loads given in Table 1 are given by the test mandrel with a minimum hardness of 45HRC and a thread tolerance of 5h6g (the major diameter is 1/4 of the lower limit of 6g) as specified in this standard.
ISO 898-1 and ISO 898-2 (GB/T 3098.1 and GB/T3098.2) mechanical property standards, ISO 4014~4018 (GB/T57805784) hexagonal head bolt standards and ISO4032~4036 (GB/T 6170, GB/T 6175, GB/T 41, GB/T 6172 and GB/T6174) hexagonal nut standards have been published. These standards reflect revised mechanical properties, nut height dimensions and modified width across flats (17, 19, 22 and 32 mm to 16, 18, 21 and 34 mm for M10, M12, M14 and M22 respectively), as recommended by [SO/TC 2].
This part of ISO 898 specifies the property classes for nuts with full load capacity as follows:
When a bolt or screw of the specified property class is matched with a nut of the corresponding property class as specified in Table 2, the load capacity of the assembly is expected to be such that the threads will not strip when the preload of the bolt or screw is equal to the proof load or yield load of the bolt. In addition, considering that overtightening is inevitable during installation, the geometric dimensions and mechanical properties of nuts up to and including size M39 and property class 12 and with thread tolerance 6H are designed to have a higher stripping strength (at least 10 % higher than the bolt breaking strength even in the most unfavourable minimum solid condition). In this way, when over-tightening occurs, the user can be warned that the installation method is improper.
Some people who use standards cannot, of course, participate in detailed research work. It is hoped that this note will help to understand the relevant difficulties. Performance level of bolts and screws
Actual maximum hardness of the screwed part of the bolt threadMaximum hardness
Performance level
335HV360HV
Maximum hardness
14—6-11
Thread specification
14—6—12
Width across flats
Height of hexagonal nut
Nut quotient m, mm
Tip: This standard content only shows part of the intercepted content of the complete standard. If you need the complete standard, please go to the top to download the complete standard document for free.