Introduction to the Standard
GB/T 5280-2002 specifies the thread dimensions and end types for self-tapping screws (sheet metal screws) with thread sizes ranging from ST1.5 to ST9.5. This standard ensures uniformity in manufacturing, facilitating reliable fastening in materials like metal sheets without pre-drilled holes.
As a key reference in mechanical fastening, it defines parameters such as pitch, major and minor diameters, and thread lengths for types C, F, and R, promoting compatibility and performance in industries including automotive, electronics, and construction. It aligns with international practices while addressing specific requirements for Chinese standards.
- Scope: Covers thread profiles for self-tapping screws in metric sizes.
- Importance: Ensures self-tapping efficiency and thread integrity.
- Updates: Superseded by later versions, but foundational for legacy designs.
Thread Specifications and Dimensions
The standard outlines thread geometry, including major diameter (d1), pitch diameter (d2), minor diameter (d3), chamfer (c), radius (r), and reference lengths (y) for different end types. These ensure proper thread formation and engagement, minimizing material damage during installation.
Key parameters include pitch varying from 0.5 mm for ST1.5 to 2.1 mm for larger sizes, with tolerances for max/min values to accommodate manufacturing variations. Type C for pointy ends, F for blunt, and R for rounded, each suited to specific material thicknesses.
Detailed Thread Table
Below is the comprehensive table of thread dimensions as per GB/T 5280-2002, providing precise values for engineering reference. Use this for design verification and production specifications.
| Parameter | ST1.5 | ST1.9 | ST2.2 | ST2.6 | ST2.9 | ST3.3 | ST3.5 | ST3.9 | ST4.2 | ST4.8 | ST5.5 | ST6.3 | ST8 | ST9.5 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Pitch | 0.5 | 0.6 | 0.8 | 0.9 | 1.1 | 1.3 | 1.3 | 1.3 | 1.4 | 1.6 | 1.8 | 1.8 | 2.1 | 2.1 |
| d1 max | 1.52 | 1.9 | 2.24 | 2.57 | 2.9 | 3.3 | 3.53 | 3.91 | 4.22 | 4.8 | 5.46 | 6.25 | 8 | 9.65 |
| d1 min | 1.38 | 1.76 | 2.1 | 2.43 | 2.76 | 3.12 | 3.35 | 3.73 | 4.04 | 4.62 | 5.28 | 6.03 | 7.78 | 9.43 |
| d2 max | 0.91 | 1.24 | 1.63 | 1.9 | 2.18 | 2.39 | 2.64 | 2.92 | 3.1 | 3.58 | 4.17 | 4.88 | 6.2 | 7.85 |
| d2 min | 0.84 | 1.17 | 1.52 | 1.8 | 2.08 | 2.29 | 2.51 | 2.77 | 2.95 | 3.43 | 3.99 | 4.7 | 5.99 | 7.59 |
| d3 max | 0.79 | 1.12 | 1.47 | 1.73 | 2.01 | 2.21 | 2.41 | 2.67 | 2.84 | 3.3 | 3.86 | 4.55 | 5.84 | 7.44 |
| d3 min | 0.69 | 1.02 | 1.37 | 1.6 | 1.88 | 2.08 | 2.26 | 2.51 | 2.69 | 3.12 | 3.68 | 4.34 | 5.64 | 7.24 |
| c max | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.15 | 0.15 | 0.15 | 0.15 | 0.15 |
| r ≈ | – | – | – | – | – | – | 0.5 | 0.6 | 0.6 | 0.7 | 0.8 | 0.9 | 1.1 | 1.4 |
| y Type C | 1.4 | 1.6 | 2 | 2.3 | 2.6 | 3 | 3.2 | 3.5 | 3.7 | 4.3 | 5 | 6 | 7.5 | 8 |
| y Type F | 1.1 | 1.2 | 1.6 | 1.8 | 2.1 | 2.5 | 2.5 | 2.7 | 2.8 | 3.2 | 3.6 | 3.6 | 4.2 | 4.2 |
| y Type R | – | – | – | – | – | – | 2.7 | 3 | 3.2 | 3.6 | 4.3 | 5 | 6.3 | – |
| Number | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 10 | 12 | 14 | 16 | 20 |
Dimensions are in mm. Select sizes based on material thickness and load requirements for optimal performance.
Application Guidelines and Considerations
When applying GB/T 5280-2002, match thread size to substrate material; smaller pitches like 0.5 mm suit thin sheets, while larger like 2.1 mm handle thicker materials. Ensure proper pilot hole sizes to avoid cracking.
- Choose Type C for soft materials requiring sharp penetration.
- Use Type F for pre-punched holes to prevent deformation.
- Apply Type R for rounded ends in sensitive applications.
- Verify tolerances during manufacturing for thread engagement.
- Consider corrosion resistance with appropriate coatings.
These guidelines enhance fastening reliability, reducing failures in assembly lines.
Frequently Asked Questions (FAQ)
What is the difference between d1, d2, and d3 in the standard?
d1 is the major diameter, d2 the pitch diameter, and d3 the minor diameter; these define the thread profile for proper fit and strength.
How do I select the appropriate thread type (C, F, R)?
Type C for pointed ends in self-piercing; Type F for blunt in pre-drilled holes; Type R for rounded to minimize damage in soft materials.
What does the ‘Number’ row represent?
It corresponds to imperial equivalents or legacy designations, aiding cross-referencing with international standards.
Are tolerances specified for these dimensions?
Yes, max/min values provide manufacturing tolerances; adhere to them for interchangeability and performance.
How has this standard evolved in later versions?
Later standards like GB/T 5280-2017 incorporate ISO alignments, expanding sizes and refining tolerances for global compatibility.
What pilot hole size is recommended for ST4.2?
Typically 3.0-3.5 mm depending on material; test for optimal engagement to ensure holding power without stripping.
