Introduction to GB/T 9145-2003 Standard
This standard specifies limit dimensions for general-purpose metric screw threads of medium accuracy in the preferred series, ensuring interchangeability and performance in mechanical assemblies. It covers coarse and fine pitch threads for internal and external applications, with tolerances applied before plating for thin coatings.
Scope
GB/T 9145-2003 defines the limit dimensions for metric screw threads with medium tolerance precision and preferred series, applicable to general engineering purposes. It ensures that thread profiles do not exceed the maximum material condition defined by basic profiles and tolerance positions. This is crucial for fasteners in industries requiring reliable mating without interference, especially post-plating.
- Applies to threads before thin coatings like electroplating.
- Post-plating, profiles must stay within H or h positions.
- Focuses on medium engagement lengths for balanced strength and manufacturability.
General Limit Dimensions
No point on the thread root profile shall exceed the maximum entity profile per basic form and tolerance. For plated threads, actual contours post-plating must not surpass H/h positions. This prevents over-tightening or failure in assemblies. Note: Tolerances suit thin platings; heavier coatings require adjustments.
Coarse Pitch Internal Threads
For medium precision, engagement length is medium. Tolerance zones: 5H for d ≤ 1.4 mm; 6H for d > 1.4 mm. Limits for pitch diameter D2 and minor diameter D1 ensure proper fit with external threads.
| Thread | Engagement Length | Pitch Diameter D2 | Minor Diameter D1 | |||
|---|---|---|---|---|---|---|
| > | ≤ | สูงสุด | นาที | สูงสุด | นาที | |
| M1 | 0.6 | 1.7 | 0.894 | 0.838 | 0.785 | 0.729 |
| M1.2 | 0.6 | 1.7 | 1.094 | 1.038 | 0.985 | 0.929 |
| M1.4 | 0.7 | 2 | 1.265 | 1.205 | 1.142 | 1.075 |
| M1.6 | 0.8 | 2.6 | 1.458 | 1.373 | 1.321 | 1.221 |
| M1.8 | 0.8 | 2.6 | 1.658 | 1.573 | 1.521 | 1.421 |
| เอ็ม2 | 1 | 3 | 1.83 | 1.74 | 1.679 | 1.567 |
| ม.2.5 | 1.3 | 3.8 | 2.303 | 2.208 | 2.138 | 2.013 |
| เอ็ม3 | 1.5 | 4.5 | 2.775 | 2.675 | 2.599 | 2.459 |
| ม3.5 | 1.7 | 5 | 3.222 | 3.11 | 3.01 | 2.85 |
| เอ็ม4 | 2 | 6 | 3.663 | 3.545 | 3.422 | 3.242 |
| เอ็ม5 | 2.5 | 7.5 | 4.605 | 4.48 | 4.334 | 4.134 |
| เอ็ม6 | 3 | 9 | 5.5 | 5.35 | 5.153 | 4.917 |
| เอ็ม7 | 3 | 9 | 6.5 | 6.35 | 6.153 | 5.917 |
| เอ็ม8 | 4 | 12 | 7.348 | 7.188 | 6.912 | 6.647 |
| เอ็ม10 | 5 | 15 | 9.206 | 9.026 | 8.676 | 8.376 |
| เอ็ม12 | 6 | 18 | 11.063 | 10.863 | 10.441 | 10.106 |
| เอ็ม14 | 8 | 24 | 12.913 | 12.701 | 12.21 | 11.835 |
| เอ็ม16 | 8 | 24 | 14.913 | 14.701 | 14.21 | 13.835 |
| เอ็ม18 | 10 | 30 | 16.6 | 16.376 | 15.744 | 15.294 |
| เอ็ม20 | 10 | 30 | 18.6 | 18.376 | 17.744 | 17.294 |
| เอ็ม22 | 10 | 30 | 20.6 | 20.376 | 19.744 | 19.294 |
| เอ็ม24 | 12 | 36 | 22.316 | 22.051 | 21.252 | 20.752 |
| เอ็ม27 | 12 | 36 | 25.316 | 25.051 | 24.252 | 23.752 |
| เอ็ม30 | 15 | 45 | 28.007 | 27.727 | 26.771 | 26.211 |
| เอ็ม33 | 15 | 45 | 31.007 | 30.727 | 29.771 | 29.211 |
| เอ็ม36 | 18 | 53 | 33.702 | 33.402 | 32.27 | 31.67 |
| เอ็ม39 | 18 | 53 | 36.702 | 36.402 | 35.27 | 34.67 |
| M42 | 21 | 63 | 39.392 | 39.077 | 37.799 | 37.129 |
| M45 | 21 | 63 | 42.392 | 42.077 | 40.799 | 40.129 |
| M48 | 24 | 71 | 45.087 | 44.752 | 43.297 | 42.587 |
| M52 | 24 | 71 | 49.087 | 48.752 | 46.681 | 45.971 |
| M56 | 28 | 85 | 52.783 | 52.428 | 50.796 | 50.046 |
| M60 | 28 | 85 | 56.783 | 56.428 | 54.796 | 54.046 |
| M64 | 32 | 95 | 60.478 | 60.103 | 58.305 | 57.505 |
These dimensions provide guidance for nut manufacturing, ensuring compatibility with bolts under medium load conditions.
Coarse Pitch External Threads
Medium precision, medium engagement. Tolerance zones: 6h for d ≤ 1.4 mm; 6g for d > 1.4 mm. Limits for major diameter d and pitch diameter d2, with min root radius per GB/T 197-2003.
| Thread | Engagement Length | Major Diameter d | Pitch Diameter d2 | Min Root Radiusเอ | |||
|---|---|---|---|---|---|---|---|
| > | ≤ | สูงสุด | นาที | สูงสุด | นาที | นาที | |
| M1 | 0.6 | 1.7 | 1 | 0.933 | 0.838 | 0.785 | 0.031 |
| M1.2 | 0.6 | 1.7 | 1.2 | 1.133 | 1.038 | 0.985 | 0.031 |
| M1.4 | 0.7 | 2 | 1.4 | 1.325 | 1.205 | 1.149 | 0.038 |
| M1.6 | 0.8 | 2.6 | 1.581 | 1.496 | 1.354 | 1.291 | 0.044 |
| M1.8 | 0.8 | 2.6 | 1.781 | 1.696 | 1.554 | 1.491 | 0.044 |
| เอ็ม2 | 1 | 3 | 1.981 | 1.886 | 1.721 | 1.654 | 0.05 |
| ม.2.5 | 1.3 | 3.8 | 2.48 | 2.38 | 2.188 | 2.117 | 0.056 |
| เอ็ม3 | 1.5 | 4.5 | 2.98 | 2.874 | 2.655 | 2.58 | 0.063 |
| ม3.5 | 1.7 | 5 | 3.479 | 3.354 | 3.089 | 3.004 | 0.075 |
| เอ็ม4 | 2 | 6 | 3.978 | 3.838 | 3.523 | 3.433 | 0.088 |
| เอ็ม5 | 2.5 | 7.5 | 4.976 | 4.826 | 4.456 | 4.361 | 0.1 |
| เอ็ม6 | 3 | 9 | 5.974 | 5.794 | 5.324 | 5.212 | 0.125 |
| เอ็ม7 | 3 | 9 | 6.974 | 6.794 | 6.324 | 6.212 | 0.125 |
| เอ็ม8 | 4 | 12 | 7.972 | 7.76 | 7.16 | 7.042 | 0.156 |
| เอ็ม10 | 5 | 15 | 9.968 | 9.732 | 8.994 | 8.862 | 0.188 |
| เอ็ม12 | 6 | 18 | 11.966 | 11.701 | 10.829 | 10.679 | 0.219 |
| เอ็ม14 | 8 | 24 | 13.962 | 13.682 | 12.663 | 12.503 | 0.25 |
| เอ็ม16 | 8 | 24 | 15.962 | 15.682 | 14.663 | 14.503 | 0.25 |
| เอ็ม18 | 10 | 30 | 17.958 | 17.623 | 16.334 | 16.164 | 0.313 |
| เอ็ม20 | 10 | 30 | 19.958 | 19.623 | 18.334 | 18.164 | 0.313 |
| เอ็ม22 | 10 | 30 | 21.958 | 21.623 | 20.334 | 20.164 | 0.313 |
| เอ็ม24 | 12 | 36 | 23.952 | 23.577 | 22.003 | 21.803 | 0.375 |
| เอ็ม27 | 12 | 36 | 26.952 | 26.577 | 25.003 | 24.803 | 0.375 |
| เอ็ม30 | 15 | 45 | 29.947 | 29.522 | 27.674 | 27.462 | 0.438 |
| เอ็ม33 | 15 | 45 | 32.947 | 32.522 | 30.674 | 30.462 | 0.438 |
| เอ็ม36 | 18 | 53 | 35.94 | 35.465 | 33.342 | 33.118 | 0.5 |
| เอ็ม39 | 18 | 53 | 38.94 | 38.465 | 36.342 | 36.118 | 0.5 |
| M42 | 21 | 63 | 41.937 | 41.437 | 39.014 | 38.778 | 0.563 |
| M45 | 21 | 63 | 44.937 | 44.437 | 42.014 | 41.778 | 0.563 |
| M48 | 24 | 71 | 47.929 | 47.399 | 44.681 | 44.431 | 0.625 |
| M52 | 24 | 71 | 51.929 | 51.399 | 48.681 | 48.431 | 0.625 |
| M56 | 28 | 85 | 55.925 | 55.365 | 52.353 | 52.088 | 0.688 |
| M60 | 28 | 85 | 59.925 | 59.365 | 56.353 | 56.088 | 0.688 |
| M64 | 32 | 95 | 63.92 | 63.32 | 60.023 | 59.743 | 0.75 |
เอ See GB/T 197-2003 Chapter 7 and Table 9 for root radius details. These ensure stress distribution and fatigue resistance.
Fine Pitch Internal Threads
Medium precision, medium engagement, 6H tolerance zone. Fine pitches offer better vibration resistance and adjustment precision.
| Thread | Engagement Length | Pitch Diameter D2 | Minor Diameter D1 | |||
|---|---|---|---|---|---|---|
| > | ≤ | สูงสุด | นาที | สูงสุด | นาที | |
| M8×1 | 3 | 9 | 7.5 | 7.35 | 7.153 | 6.917 |
| M10×1 | 4 | 12 | 9.5 | 9.35 | 9.153 | 8.917 |
| M10×1.25 | 4 | 12 | 9.348 | 9.188 | 8.912 | 8.647 |
| M12×1.25 | 4.5 | 13 | 11.368 | 11.188 | 10.912 | 10.647 |
| M12×1.5 | 4.5 | 13 | 11.216 | 11.026 | 10.676 | 10.376 |
| M14×1.5 | 5.6 | 16 | 13.216 | 13.026 | 12.676 | 12.376 |
| M16×1.5 | 5.6 | 16 | 15.216 | 15.026 | 14.676 | 14.376 |
| M18×1.5 | 5.6 | 16 | 17.216 | 17.026 | 16.676 | 16.376 |
| M18×2 | 5.6 | 16 | 16.913 | 16.701 | 16.21 | 15.835 |
| M20×1.5 | 5.6 | 16 | 19.216 | 19.026 | 18.676 | 18.376 |
| M20×2 | 5.6 | 16 | 18.913 | 18.701 | 18.21 | 17.835 |
| M22×1.5 | 5.6 | 16 | 21.216 | 21.026 | 20.676 | 20.376 |
| M22×2 | 5.6 | 16 | 20.913 | 20.701 | 20.21 | 19.835 |
| M24×2 | 8.5 | 25 | 22.925 | 22.701 | 22.21 | 21.835 |
| M27×2 | 8.5 | 25 | 25.925 | 25.701 | 25.21 | 24.835 |
| M30×2 | 8.5 | 25 | 28.925 | 28.701 | 28.21 | 27.835 |
| M33×2 | 8.5 | 25 | 31.925 | 31.701 | 31.21 | 30.835 |
| M36×3 | 12 | 36 | 34.316 | 34.051 | 33.252 | 32.752 |
| M39×3 | 12 | 36 | 37.316 | 37.051 | 36.252 | 35.752 |
| M42×3 | 12 | 36 | 40.316 | 40.051 | 39.252 | 38.752 |
| M45×3 | 12 | 36 | 43.316 | 43.051 | 42.252 | 41.752 |
| M48×3 | 15 | 45 | 46.331 | 46.051 | 45.252 | 44.752 |
| M52×4 | 19 | 56 | 49.717 | 49.402 | 48.27 | 47.67 |
| M56×4 | 19 | 56 | 53.717 | 53.402 | 52.27 | 51.67 |
| M60×4 | 19 | 56 | 57.717 | 57.402 | 56.27 | 55.67 |
| M64×4 | 19 | 56 | 61.717 | 61.402 | 60.27 | 59.67 |
These values support finer load distribution in high-vibration environments.
Fine Pitch External Threads
Medium precision, medium engagement, 6g tolerance zone. Provides stronger core sections for enhanced shear strength.
| Thread | Engagement Length | Major Diameter d | Pitch Diameter d2 | Min Root Radiusเอ | |||
|---|---|---|---|---|---|---|---|
| > | ≤ | สูงสุด | นาที | สูงสุด | นาที | นาที | |
| M8×1 | 3 | 9 | 7.974 | 7.794 | 7.324 | 7.212 | 0.125 |
| M10×1 | 4 | 12 | 9.974 | 9.794 | 9.324 | 9.212 | 0.125 |
| M10×1.25 | 4 | 12 | 9.972 | 9.76 | 9.16 | 9.042 | 0.156 |
| M12×1.25 | 4.5 | 13 | 11.972 | 11.76 | 11.16 | 11.028 | 0.156 |
| M12×1.5 | 4.5 | 13 | 11.968 | 11.732 | 10.994 | 10.854 | 0.188 |
| M14×1.5 | 5.6 | 16 | 13.968 | 13.732 | 12.994 | 12.854 | 0.188 |
| M16×1.5 | 5.6 | 16 | 15.968 | 15.732 | 14.994 | 14.854 | 0.188 |
| M18×1.5 | 5.6 | 16 | 17.968 | 17.732 | 16.994 | 16.854 | 0.188 |
| M18×2 | 5.6 | 16 | 17.962 | 17.682 | 16.663 | 16.503 | 0.25 |
| M20×1.5 | 5.6 | 16 | 19.968 | 19.732 | 18.994 | 18.854 | 0.188 |
| M20×2 | 5.6 | 16 | 19.962 | 19.682 | 18.663 | 18.503 | 0.25 |
| M22×1.5 | 5.6 | 16 | 21.968 | 21.732 | 20.994 | 20.854 | 0.188 |
| M22×2 | 5.6 | 16 | 21.962 | 21.682 | 20.663 | 20.503 | 0.25 |
| M24×2 | 8.5 | 25 | 23.962 | 23.682 | 22.663 | 22.493 | 0.25 |
| M27×2 | 8.5 | 25 | 26.962 | 26.682 | 25.663 | 25.493 | 0.25 |
| M30×2 | 8.5 | 25 | 29.962 | 29.682 | 28.663 | 28.493 | 0.25 |
| M33×2 | 8.5 | 25 | 32.962 | 32.682 | 31.663 | 31.493 | 0.25 |
| M36×3 | 12 | 36 | 35.952 | 35.577 | 34.003 | 33.803 | 0.375 |
| M39×3 | 12 | 36 | 38.952 | 38.577 | 37.003 | 36.803 | 0.375 |
| M42×3 | 12 | 36 | 41.952 | 41.577 | 40.003 | 39.803 | 0.375 |
| M45×3 | 12 | 36 | 44.952 | 44.577 | 43.003 | 42.803 | 0.375 |
| M48×3 | 15 | 45 | 47.952 | 47.577 | 46.003 | 45.791 | 0.375 |
| M52×4 | 19 | 56 | 51.94 | 51.465 | 49.342 | 49.106 | 0.5 |
| M56×4 | 19 | 56 | 55.94 | 55.465 | 53.342 | 53.106 | 0.5 |
| M60×4 | 19 | 56 | 59.94 | 59.465 | 57.342 | 57.106 | 0.5 |
| M64×4 | 19 | 56 | 63.94 | 63.465 | 61.342 | 61.106 | 0.5 |
เอ See GB/T 197-2003 for root radius specifications, critical for avoiding stress concentrations.
คำถามที่พบบ่อย
What tolerance zones apply to coarse internal threads?
5H for diameters ≤1.4 mm; 6H for >1.4 mm, ensuring medium precision fit.
How does plating affect thread dimensions?
Tolerances are pre-plating; post-plating profiles must not exceed H/h positions for thin coatings to maintain assembly.
Why use fine pitch threads?
They provide better vibration resistance and finer adjustments, with stronger cores per limits in tables 3 and 4.
What is medium engagement length?
It balances thread strength and cost; use table values for specific ranges to avoid over- or under-engagement.
How to interpret root radius?
Min values per GB/T 197-2003 reduce stress; essential for fatigue-prone applications.
Are these limits for all materials?
Yes, but adjust for special platings; consult standard for heavy coatings requiring oversized threads.
