+86-18925741509 Evan.xiao@bomeihardware.com

Bomei Precision Machining Co., Ltd

Resources


Home>Resources>

Blog

A Guide To 6H and 6g Tolerance Classes for Internal and External Threads

2025-03-15 09:33:36

In the world of manufacturing and engineering, the precision of threads is of utmost importance. Tolerance classes play a crucial role in ensuring that internal and external threads fit together correctly. Among the various tolerance classes available, 6H and 6g are two commonly used classes for internal and external threads respectively, Although other classes 4g, 5g & 7g and 4H, 5H & 7H are also used.

By understanding these tolerances, you can ensure that your threaded assemblies are reliable and efficient.

1.Definition of 6H and 6g Tolerance Classes

6H Tolerance Class for Internal Threads

The 6H tolerance class is used for internal threads. In this class, the "6" represents the tolerance grade, which indicates the allowable variation in the thread dimensions. The "H" indicates the basic deviation, which is the position of the tolerance zone relative to the basic size. For internal threads, the H basic deviation is always zero, meaning that the tolerance zone is located above the basic size. This means that the minimum size of the internal thread is equal to the basic size, and the maximum size is the basic size plus the tolerance.


Metric Internal Thread Tolerances Chart (Nuts)

Thread Size

Tolerance

Minor Diameter

Pitch Diameter

Major Diameter

x Thread Pitch

Class

min.

max.

min.

max.

min.

max.

M1.6 x 0.35

6H

1.221

1.321

1.373

1.458

1.6

1.736

M2 x 0.4

6H

1.567

1.679

1.74

1.83

2

2.148

M2.5 x 0.45

6H

2.013

2.138

2.208

2.303

2.5

2.66

M3 x 0.5

6H

2.459

2.599

2.675

2.775

3

3.172

M3.5 x 0.6

6H

2.85

3.01

3.11

3.222

3.5

3.698

M4 x 0.7

6H

3.242

3.422

3.545

3.663

4

4.219

M5 x 0.8

6H

4.134

4.334

4.48

4.605

5

5.24

M6 x 1

6H

4.917

5.153

5.35

5.5

6

6.294

M8 x 1.25

6H

6.647

6.912

7.188

7.348

8

8.34

M8 x 1

6H

6.917

7.153

7.35

7.5

8

8.294

M10 x 1.5

6H

8.376

8.676

9.026

9.206

10

10.397

M10 x 1.25

6H

8.647

8.912

9.188

9.348

10

10.34

M10 x 1

6H

8.917

9.153

9.35

9.5

10

10.294

M10 x 0.75

6H

9.188

9.378

9.513

9.645

10

10.24

M12 x 1.75

6H

10.106

10.441

10.863

11.063

12

12.452

M12 x 1.5

6H

10.376

10.676

11.026

11.216

12

12.407

M12 x 1.25

6H

10.647

10.912

11.188

11.368

12

12.36

M12 x 1

6H

10.917

11.153

11.35

11.51

12

12.304

M14 x 2

6H

11.835

12.21

12.701

12.913

14

14.501

M14 x 1.5

6H

12.376

12.676

13.026

13.216

14

14.407

M15 x 1

6H

13.917

14.153

14.35

14.51

15

15.304

M16 x 2

6H

13.835

14.21

14.701

14.913

16

16.501

M16 x 1.5

6H

14.376

14.676

15.026

15.216

16

16.407

M17 x 1

6H

15.917

16.153

16.35

16.51

17

17.304

M18 x 1.5

6H

16.376

16.676

17.026

17.216

18

18.407

M20 x 2.5

6H

17.294

17.744

18.376

18.6

20

20.585

M20 x 1.5

6H

18.376

18.676

19.026

19.216

20

20.407

M20 x 1

6H

18.917

19.153

19.35

19.51

20

20.304

M22 x 2.5

6H

19.294

19.744

20.376

20.6

22

22.585

M22 x 1.5

6H

20.376

20.676

21.026

21.216

22

22.407

M24 x 3

6H

20.752

21.252

22.051

22.316

24

24.698

M24 x 2

6H

21.835

22.21

22.701

22.925

24

24.513

M25 x 1.5

6H

23.376

23.676

24.026

24.226

25

25.417

M27 x 3

6H

23.752

24.252

25.051

25.316

27

27.698

M27 x 2

6H

24.835

25.21

25.701

25.925

27

27.513

M30 x 3.5

6H

26.211

26.771

27.727

28.007

30

30.786

M30 x 2

6H

27.835

28.21

28.701

28.925

30

30.513

M30 x 1.5

6H

28.376

28.676

29.026

29.226

30

30.417

M33 x 2

6H

30.835

31.21

31.701

31.925

33

33.513

M35 x 1.5

6H

33.376

33.676

34.026

34.226

35

35.417

M36 x 4

6H

31.67

32.27

33.402

33.702

36

36.877

M36 x 2

6H

33.835

34.21

34.701

34.925

36

36.513

M39 x 2

6H

36.835

37.21

37.701

37.925

39

39.513

M40 x 1.5

6H

38.376

38.676

39.026

39.226

40

40.417

M42 x 4.5

6H

37.129

37.799

39.077

39.392

42

42.964

M42 x 2

6H

39.835

40.21

40.701

40.925

42

42.513

M45 x 1.5

6H

43.376

43.676

44.026

44.226

45

45.417

M48 x 5

6H

42.587

43.297

44.752

45.087

48

49.056

M48 x 2

6H

45.835

46.21

46.701

46.937

48

48.525

M50 x 1.5

6H

48.376

48.676

49.026

49.238

50

50.429

M55 x 1.5

6H

53.376

53.676

54.026

54.238

55

55.429

M56 x 5.5

6H

50.046

50.796

52.428

52.783

56

57.149

M56 x 2

6H

53.835

54.21

54.701

54.937

56

56.525

M60 x 1.5

6H

58.376

58.676

59.026

59.238

60

60.429

6g Tolerance Class for External Threads

The 6g tolerance class is used for external threads. Similar to the 6H class, the "6" represents the tolerance grade, and the "g" indicates the basic deviation. For external threads, the g basic deviation is negative, which means that the tolerance zone is located below the basic size. This implies that the maximum size of the external thread is equal to the basic size, and the minimum size is the basic size minus the tolerance.

Metric External Thread Tolerances Chart (Bolt or Screw Thread)

Thread Size

Tolerance

Major Diameter

Pitch Diameter

Minor Diameter

x Thread Pitch

Class

max.

min.

max.

min.

max.

min.

M1.6 x 0.35

6g

1.581

1.496

1.354

1.291

1.202

1.075

M2 x 0.4

6g

1.981

1.886

1.721

1.654

1.548

1.408

M2.5 x 0.45

6g

2.48

2.38

2.188

2.117

1.993

1.84

M3 x 0.5

6g

2.98

2.874

2.655

2.58

2.438

2.272

M3.5 x 0.6

6g

3.479

3.354

3.089

3.004

2.829

2.634

M4 x 0.7

6g

3.978

3.838

3.523

3.433

3.22

3.002

M5 x 0.8

6g

4.976

4.826

4.456

4.361

4.11

3.868

M6 x 1

6g

5.974

5.794

5.324

5.212

4.891

4.596

M7 x 1

6g

6.974

6.794

6.324

6.212

5.891

5.596

M8 x 0.75

6g

7.978

7.838

7.491

7.391

7.166

6.929

M8 x 1

6g

7.974

7.794

7.324

7.212

6.891

6.596

M8 x 1.25

6g

7.972

7.76

7.16

7.042

6.619

6.272

M10 x 0.75

6g

9.978

9.838

9.491

9.391

9.166

8.929

M10 x 1

6g

9.974

9.794

9.324

9.212

8.891

8.596

M10 x 1.25

6g

9.972

9.76

9.16

9.042

8.619

8.272

M10 x 1.5

6g

9.968

9.732

8.994

8.862

8.344

7.938

M12 x 1

6g

11.974

11.794

11.324

11.206

10.891

10.59

M12 x 1.25

6g

11.972

11.76

11.16

11.028

10.619

10.258

M12 x 1.5

6g

11.968

11.732

10.994

10.854

10.344

9.93

M12 x 1.75

6g

11.966

11.701

10.829

10.679

10.071

9.601

M14 x 1.5

6g

13.968

13.732

12.994

12.854

12.344

11.93

M14 x 2

6g

13.962

13.682

12.663

12.503

11.797

11.271

M16 x 1.5

6g

15.968

15.732

14.994

14.854

14.344

13.93

M16 x 2

6g

15.962

15.682

14.663

14.503

13.797

13.271

M18 x 1

6g

17.974

17.794

17.324

17.206

16.891

16.59

M18 x 1.5

6g

17.968

17.732

16.994

16.854

16.344

15.93

M20 x 1

6g

19.974

19.794

19.324

19.206

18.891

18.59

M20 x 1.5

6g

19.968

19.732

18.994

18.854

18.344

17.93

M20 x 2.5

6g

19.958

19.623

18.334

18.164

17.251

16.624

M22 x 1.5

6g

21.968

21.732

20.994

20.854

20.344

19.93

M22 x 2.5

6g

21.958

21.623

20.334

20.164

19.251

18.624

M24 x 2

6g

23.962

23.682

22.663

22.493

21.797

21.261

M24 x 3

6g

23.952

23.577

22.003

21.803

20.704

19.955

M27 x 2

6g

26.962

26.682

25.663

25.493

24.797

24.261

M27 x 3

6g

26.952

26.577

25.003

24.803

23.704

22.955

M30 x 1.5

6g

29.968

29.732

28.994

28.844

28.344

27.92

M30 x 2

6g

29.962

29.682

28.663

28.493

27.797

27.261

M30 x 3.5

6g

29.947

29.522

27.674

27.462

26.158

25.306

M32 x 2

6g

31.962

31.682

30.663

30.493

29.797

29.261

M33 x 2

6g

32.962

32.682

31.663

31.493

30.797

30.261

M35 x 1.5

6g

34.968

34.732

33.994

33.844

33.344

32.92

M36 x 2

6g

35.962

35.682

34.663

34.493

33.797

33.261

M36 x 4

6g

35.94

35.465

33.342

33.118

31.61

30.654

M39 x 2

6g

38.962

38.682

37.663

37.493

36.797

36.261

M40 x 1.5

6g

39.968

39.732

38.994

38.844

38.344

37.92

M42 x 2

6g

41.962

41.682

40.663

40.493

39.797

39.261

M42 x 4.5

6g

41.937

41.437

39.014

38.778

37.065

36.006

M45 x 1.5

6g

44.968

44.732

43.994

43.844

43.344

42.92

M48 x 2

6g

47.962

47.682

46.663

46.483

45.797

45.251

M48 x 5

6g

47.929

47.399

44.681

44.431

42.516

41.351

M50 x 1.5

6g

49.968

49.732

48.994

48.834

48.344

47.91

M55 x 1.5

6g

54.968

54.732

53.994

53.834

53.344

52.91

M56 x 2

6g

55.962

55.682

54.663

54.483

53.797

53.251

M56 x 5.5

6g

55.925

55.365

52.353

52.088

49.971

48.7

M60 x 1.5

6g

59.968

59.732

58.994

58.834

58.344

57.91


 

2.Differences between 6H and 6g Tolerance Classes

Tolerance Zone Position

As mentioned earlier, the main difference between 6H and 6g tolerance classes lies in the position of the tolerance zone. The 6H tolerance zone for internal threads is above the basic size, while the 6g tolerance zone for external threads is below the basic size. This difference in position ensures a proper fit between the internal and external threads.

Allowable Variation

The tolerance values for 6H and 6g classes are also different. The tolerance for 6H internal threads is typically smaller than that for 6g external threads. This is because internal threads need to be more precise to ensure a proper fit with the external threads. The smaller tolerance for internal threads helps to prevent loose fits or leaks in applications where threads are used for sealing or fastening.

Fit Characteristics

The combination of 6H internal threads and 6g external threads provides a medium fit. This means that the fit is neither too loose nor too tight. It allows for easy assembly and disassembly of parts while still providing sufficient strength and stability. In some applications, a different fit may be required, such as a tight fit for high - pressure applications or a loose fit for applications where ease of assembly is more important.

3.Industry of Application

Automotive Industry

In the automotive industry, 6H and 6g tolerance classes are widely used for various applications. For example, they are used in engine components such as bolts, nuts, and studs. The precise fit provided by these tolerance classes ensures the proper functioning of the engine and helps to prevent leaks and vibrations. They are also used in transmission systems, suspension components, and other automotive parts where threaded connections are required.

Aerospace Industry

The aerospace industry requires the highest level of precision in manufacturing. 6H and 6g tolerance classes are used in aerospace applications where threads need to be extremely precise. For example, they are used in aircraft engines, landing gear systems, and structural components. The tight tolerances ensure the safety and reliability of the aircraft, as any small deviation in the thread dimensions could potentially lead to catastrophic failures.

Machinery and Equipment Manufacturing

In the machinery and equipment manufacturing industry, 6H and 6g tolerance classes are used in a wide range of applications. They are used in machinery such as pumps, valves, and compressors, where threaded connections are used to assemble and disassemble the components. The proper fit provided by these tolerance classes ensures the smooth operation of the machinery and helps to prevent leaks and failures. They are also used in industrial equipment such as conveyors, cranes, and forklifts, where threaded connections are used for structural and functional purposes.

Plumbing and Pipe Fitting

In the plumbing and pipe fitting industry, 6H and 6g tolerance classes are used for threaded connections in pipes and fittings. The precise fit provided by these tolerance classes ensures a leak - free connection between the pipes and fittings. This is important in plumbing systems to prevent water leaks and ensure the proper flow of water. They are also used in gas piping systems, where a tight fit is required to prevent gas leaks.

 

4.Importance of 6H and 6g Tolerance Classes

Ensuring Proper Fit

The primary importance of 6H and 6g tolerance classes is to ensure a proper fit between internal and external threads. A proper fit is essential for the functionality and performance of the threaded connection. If the threads do not fit properly, it can lead to issues such as leaks, vibrations, and loosening of the connection. By using the correct tolerance classes, manufacturers can ensure that the threads fit together correctly and provide the required strength and stability.

Preventing Leaks

In applications where threads are used for sealing, such as in plumbing and gas piping systems, the proper fit provided by 6H and 6g tolerance classes is crucial for preventing leaks. A tight fit between the internal and external threads helps to create a seal that prevents the leakage of fluids or gases. This is important for the safety and efficiency of the system.

Enhancing Product Performance

The use of 6H and 6g tolerance classes can also enhance the performance of the product. A precise fit between the threads can reduce friction and wear, which can improve the efficiency and lifespan of the product. It can also reduce the risk of vibrations and noise, which can improve the comfort and reliability of the product.

Meeting Industry Standards

In many industries, there are specific standards and regulations that govern the use of threads. By using 6H and 6g tolerance classes, manufacturers can ensure that their products meet these standards and regulations. This is important for the safety and quality of the products and can also help to avoid legal issues.

 

In conclusion, 6H and 6g tolerance classes are important for ensuring the precision and functionality of internal and external threads. They play a crucial role in various industries, including automotive, aerospace, machinery and equipment manufacturing, and plumbing and pipe fitting. By understanding the definition, differences, applications, and importance of these tolerance classes, manufacturers can produce high - quality products that meet the required standards and regulations.

Related news

Contact us

Start a pleasant cooperation

Dongguan Bomei Precision Machining Co., Ltd

Address: 101, No68, Ditangshan Road 2,Dalingshan Town, Dongguan, Guangdong, China

Contact person: Evan Xiao
Mob/WhatsApp:+86-18925741509
E-mail: Evan.xiao@bomeihardware.com


About us
Who Are WeCompetenciesQuality ManagementProduct Equipment
Services
CNC MachiningSheet Metal FabricationSurface Finishing
Resources
BlogFAQVideosGallery
Link:
admin|BOMEI Plastic Hardware Limited|
CopyRight©Bomei Plastic Hardware Limited
Support: buhuyo.com
Tel E-mail