Introduction to Combination Screws
Combination screws, as defined in the GB 9074 series, are integrated fastening assemblies consisting of a screw, spring washer, and flat washer. These standards ensure uniformity in design, dimensions, and performance for reliable use in mechanical and electrical applications. GB9074.4 covers cross recessed pan head screws with washers, GB9074.8 addresses cross recessed small pan head variants, and GB9074.13 specifies cross recessed hexagon head assemblies. These screws are engineered to provide anti-loosening properties through the incorporated washers, enhancing joint integrity under vibration or dynamic loads.
In manufacturing, stainless steel grades like SUS304 and SUS316 predominate for corrosion resistance, while carbon steel options (e.g., 1010, 1018, 10B21) are available for higher strength requirements, though they necessitate heat treatment and plating processes. This guide draws from established national standards to offer detailed specifications, aiding engineers in selection and application for optimal performance and compliance.
Types and Configurations
Combination screws vary by head style and assembly components:
- Pan Head (GB9074.4): Features a larger, thicker head for broader load distribution, based on GB818 cross recessed pan head screws.
- Small Pan Head (GB9074.8): Has a smaller, thinner head compared to GB9074.4, aligned with GB823 cross recessed small pan head screws, suitable for space-constrained installations.
- Hexagon Head with Cross Recess (GB9074.13): Combines hexagonal torque application with cross recess, following GB29.2 standards, ideal for high-torque needs.
Each type includes a spring washer (GB9074.26) and flat washer (GB9074.24 or GB97.4), custom-designed for combination use rather than standard off-the-shelf parts, ensuring precise fit and functionality.
Dimensional Specifications for GB9074.4
GB9074.4 specifies dimensions for cross recessed pan head combination screws. The screw component adheres to GB818, with assemblies extending from 5 mm to 90 mm in length, surpassing standard ranges for versatility. Key parameters include thread pitch, head diameter (dk), head height (k), and recess details. All measurements are in millimeters.
| Thread Specification d | M2.5 | M3 | M3.5 | M4 | M5 | M6 | M8 | ||
|---|---|---|---|---|---|---|---|---|---|
| Pitch p | 0.45 | 0.5 | 0.6 | 0.7 | 0.8 | 1 | 1.25 | ||
| Head Diameter dk | max | 5 | 5.6 | 7 | 8 | 9.5 | 12 | 16 | |
| min | 4.7 | 5.3 | 6.64 | 7.64 | 9.14 | 11.57 | 15.57 | ||
| Head Thickness k | max | 2.1 | 2.4 | 2.6 | 3.1 | 3.7 | 4.6 | 6 | |
| min | 1.96 | 2.26 | 2.46 | 2.92 | 3.52 | 4.3 | 5.7 | ||
| Cross Recess | Recess No. | 1 | 2 | 2 | 2 | 2 | 3 | 4 | |
| Penetration Depth | max | 1.55 | 1.43 | 1.9 | 2.4 | 2.9 | 3.6 | 4.6 | |
| min | 1.15 | 0.86 | 1.4 | 1.9 | 2.4 | 3.1 | 4 | ||
| Width m | 2.7 | 3.5 | 3.9 | 4.4 | 4.9 | 6.9 | 9 | ||
| Length L | 6-25 | 6-30 | 6-60 | 6-60 | 8-60 | 10-60 | 12-40 | ||
These dimensions ensure compatibility; for extended lengths up to 90 mm, consult manufacturers for custom production.
Dimensional Specifications for GB9074.8
GB9074.8 outlines specs for cross recessed small pan head combination screws, with heads smaller and thinner than GB9074.4. Based on GB823, lengths range from 6 mm to 60 mm standard, extendable to 90 mm. Note recess differences: M5 uses No. 3 in GB9074.8 vs. No. 2 in GB9074.4.
| Nominal Diameter d | M2 | M3 | M4 | M5 | M6 | M8 | |
|---|---|---|---|---|---|---|---|
| Pitch P | 0.4 | 0.5 | 0.7 | 0.8 | 1 | 1.25 | |
| dk | max | 3.5 | 5.5 | 7.0 | 9.0 | 10.5 | 14.0 |
| min | 3.2 | 5.2 | 6.64 | 8.64 | 10.07 | 13.57 | |
| k | max | 1.4 | 2.15 | 2.75 | 3.45 | 4.1 | 5.4 |
| min | 1.26 | 2.01 | 2.61 | 3.27 | 3.8 | 5.1 | |
| Recess No. | 1 | 2 | 3 | ||||
| Length L | 6-25 | 6-30 | 6-60 | 8-60 | 10-60 | 12-40 | |
Select based on space constraints; verify recess compatibility with drivers.
Dimensional Specifications for GB9074.13
GB9074.13 details cross recessed hexagon head combination screws, combining hex and cross drives per GB29.2. Lengths span 6 mm to 50 mm, suitable for torque-intensive tasks.
| Nominal Diameter d | M4 | M5 | M6 | M8 | |
|---|---|---|---|---|---|
| Pitch p | 0.7 | 0.8 | 1 | 1.25 | |
| k | Nominal | 2.8 | 3.5 | 4 | 5.3 |
| max | 3 | 3.74 | 4.24 | 5.54 | |
| min | 2.6 | 3.26 | 3.76 | 5.06 | |
| dk | max | 7 | 8 | 10 | 13 |
| min | 6.64 | 7.64 | 9.64 | 12.57 | |
| Length L | 6-40 | 10-40 | 10-50 | 12-40 | |
These provide dual drive options, enhancing installation flexibility.
Specifications for Washers (GB9074.26, GB9074.24, GB97.4)
Washers are integral: GB9074.26 for spring washers, GB9074.24 for flat washers (default), and GB97.4 offering series variations (small, standard, large).
GB9074.26 Spring Washer
| Size | d | s | b | h | ||||
|---|---|---|---|---|---|---|---|---|
| min | max | min | max | min | max | min | max | |
| 2.5 | 2.2 | 2.34 | 0.52 | 0.68 | 0.9 | 1.1 | 1.2 | 1.5 |
| 3 | 2.69 | 2.83 | 0.7 | 0.9 | 1.1 | 1.3 | 1.6 | 2 |
| 4 | 3.6 | 3.78 | 1 | 1.2 | 1.4 | 1.6 | 2.2 | 2.75 |
| 5 | 4.45 | 4.75 | 1.2 | 1.4 | 1.9 | 2.1 | 2.6 | 3.25 |
| 6 | 5.41 | 5.71 | 1.5 | 1.7 | 2.35 | 2.65 | 3.2 | 4 |
| 8 | 7.28 | 7.64 | 1.9 | 2.1 | 2.85 | 3.15 | 4 | 5 |
| 10 | 9.23 | 9.59 | 2.35 | 2.65 | 3.3 | 3.7 | 5 | 6.25 |
| 12 | 11.1 | 11.53 | 2.85 | 3.15 | 3.8 | 4.2 | 6 | 7.5 |
GB9074.24 Flat Washer
| d | Nominal | 2.5 | 3 | 4 | 5 | 6 | 8 | 10 | 12 |
|---|---|---|---|---|---|---|---|---|---|
| Inner Diameter | max | 2.34 | 2.83 | 3.78 | 4.75 | 5.71 | 7.64 | 9.59 | 11.53 |
| min | 2.24 | 2.73 | 3.66 | 4.57 | 5.53 | 7.42 | 9.37 | 11.26 | |
| Outer Diameter d1 | max | 6 | 7 | 9 | 10 | 12 | 16 | 20 | 24 |
| min | 5.7 | 6.64 | 8.64 | 9.64 | 11.57 | 15.57 | 19.48 | 23.48 | |
| Thickness h | Nominal | 0.5 | 0.5 | 0.8 | 1 | 1.6 | 2 | 2.5 | 3 |
| max | 0.55 | 0.55 | 0.9 | 1.1 | 1.8 | 2.2 | 2.7 | 3.3 | |
| min | 0.45 | 0.45 | 0.7 | 0.9 | 1.4 | 1.8 | 2.3 | 2.7 |
GB97.4 Flat Washer
| Thread d | Small Series | Standard Series | Large Series | |||
|---|---|---|---|---|---|---|
| h Nominal | d1 max | h Nominal | d1 max | h Nominal | d1 max | |
| M2 | 0.6 | 4.5 | 0.6 | 5 | 0.6 | 6 |
| M2.5 | 0.6 | 5 | 0.6 | 6 | 0.6 | 8 |
| M3 | 0.6 | 6 | 0.6 | 7 | 0.8 | 9 |
| M3.5 | 0.8 | 7 | 0.8 | 8 | 0.8 | 11 |
| M4 | 0.8 | 8 | 0.8 | 9 | 1 | 12 |
| M5 | 1 | 9 | 1 | 10 | 1 | 15 |
| M6 | 1.6 | 11 | 1.6 | 12 | 1.6 | 18 |
| M8 | 1.6 | 15 | 1.6 | 16 | 2 | 24 |
| M10 | 2 | 18 | 2 | 20 | 2.5 | 30 |
| M12 | 2 | 20 | 2.5 | 24 | 3 | 37 |
Specify series for GB97.4; default is GB9074.24 for standard applications.
Materials and Chemical Compositions
Materials include stainless steels SUS304 and SUS316 for corrosion resistance, and carbon steels (1010, 1018, 10B21) for strength, with grades 4.8 and 8.8. Carbon steel requires hardening, dehydrogenation, and plating, unlike stainless which needs only cleaning.
| Material | C (%) | Mn (%) | Si (%) | P (%) | S (%) | Ni (%) | Mo (%) | Cr (%) |
|---|---|---|---|---|---|---|---|---|
| SUS304 Stainless Steel | ≤0.08 | ≤2.00 | ≤1.00 | ≤0.045 | ≤0.03 | 8.00-11.00 | – | 17.00-19.00 |
| SUS316 Stainless Steel | ≤0.08 | ≤2.00 | ≤1.00 | ≤0.045 | ≤0.03 | 10.00-14.00 | 2.00-3.00 | 16.00-18.00 |
SUS316 excels in marine environments; carbon steel suits high-load scenarios with proper treatment.
Performance Characteristics
Stainless combination screws typically achieve A2-70 or A4-70 performance, with tensile strength around 700 MPa and yield of 450 MPa. Carbon steel variants reach 4.8 (400 MPa tensile) or 8.8 (800 MPa). The spring washer provides locking, resisting vibration per standard tests.
Advantages and Applications
Advantages include pre-assembly for efficiency, anti-loosening, and corrosion resistance. Applications: GB9074.4/8 in electronics and communications; GB9074.13 in railways, bridges, and construction for high-strength needs.
Installation and Manufacturing Considerations
Install with appropriate drivers, ensuring washers seat properly. For carbon steel, minimum order quantities apply due to processing. Stainless production is streamlined, ideal for quick turnaround.
Frequently Asked Questions (FAQ)
What distinguishes GB9074.4 from GB9074.8?
GB9074.4 has larger, thicker heads for better load distribution; GB9074.8 features smaller heads for compact spaces, with differing recess sizes for M5 (No. 2 vs. No. 3).
When to choose SUS316 over SUS304?
Opt for SUS316 in corrosive environments like marine or chemical exposure due to its molybdenum content enhancing pitting resistance.
Can lengths exceed standard ranges?
Yes, custom lengths up to 90 mm are possible, though standard is 6-60 mm; specify for manufacturing feasibility.
What washer series to select for GB97.4?
Choose small for tight spaces, standard for general use, large for broad load spreading; default is GB9074.24 unless specified.
How does carbon steel processing differ from stainless?
Carbon steel requires hardening, dehydrogenation, and plating for durability, while stainless needs only cleaning, making it simpler and faster to produce.
Are these screws suitable for high-vibration applications?
Yes, the integrated spring washer provides effective locking; test per standards for specific vibration profiles.
