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Fastener Manufacturer Direct Black Oxide/Zinc CSK Flat Head Hex Socket Bolt Screws are countersunk - head fasteners with internal hex sockets, designed for flush - mounted installations. Made from carbon steel (available in strength grades 4.8, 8.8, 10.9), they feature two surface treatments: black oxide for wear resistance and low light reflection (ideal for machinery), and black zinc plating for enhanced rust protection (suited for damp environments). Compliant with standards like DIN7991, they come in sizes from M2 to M24. The CSK head sits flush with the workpiece, making them perfect for electronics enclosures, furniture assembly, automotive interiors, and industrial machinery panels, where a smooth, snag - free surface and corrosion resistance matter.
Instructions for Use：
Install using a matching hex socket wrench, tightening until the CSK head is fully flush (avoid over - tightening to prevent warping). For maintenance: Clean regularly with a dry cloth. Repair scratched black oxide/zinc coating promptly with anti - rust paint. Avoid long - term exposure to strong acids or saltwater, as these can damage the finish.
| Screw Thread | M3 | M4 | M5 | M6 | M8 | M10 | M12 | (M14) | M16 | M20 | M24 | |
| d | ||||||||||||
| P | Pitch | 0.5 | 0.7 | 0.8 | 1 | 1.25 | 1.5 | 1.75 | 2 | 2 | 2.5 | 3 |
| α | tol.(+2) | 90° | 90° | 90° | 90° | 90° | 90° | 90° | 90° | 90° | 90° | 60° |
| b | L≤125 | 12 | 14 | 16 | 18 | 22 | 26 | 30 | 34 | 38 | 46 | 54 |
| 125＜L ≤ 200 | / | / | / | 24 | 28 | 32 | 36 | 40 | 44 | 52 | 60 | |
| L＞200 | / | / | / | / | / | 45 | 49 | 53 | 57 | 65 | 73 | |
| dk | max=nominal size | 6 | 8 | 10 | 12 | 16 | 20 | 24 | 27 | 30 | 36 | 39 |
| min | 5.7 | 7.64 | 9.64 | 11.57 | 15.57 | 19.48 | 23.48 | 26.48 | 29.48 | 35.38 | 38.38 | |
| ds | max=nominal size | 3 | 4 | 5 | 6 | 8 | 10 | 12 | 14 | 16 | 20 | 24 |
| min | 2.86 | 3.82 | 4.82 | 5.82 | 7.78 | 9.78 | 11.73 | 13.73 | 15.73 | 19.67 | 23.67 | |
| e | min | 2.3 | 2.87 | 3.44 | 4.58 | 5.72 | 6.86 | 9.15 | 11.43 | 11.43 | 13.72 | 16 |
| k | max | 1.7 | 2.3 | 2.8 | 3.3 | 4.4 | 5.5 | 6.5 | 7 | 7.5 | 8.5 | 14 |
| s | Nominal Size | 2 | 2.5 | 3 | 4 | 5 | 6 | 8 | 10 | 10 | 12 | 14 |
| min | 2.02 | 2.52 | 3.02 | 4.02 | 5.02 | 6.02 | 8.025 | 10.025 | 10.025 | 12.032 | 14.032 | |
| max | 2.1 | 2.6 | 3.1 | 4.12 | 5.14 | 6.14 | 8.175 | 10.175 | 10.175 | 12.212 | 14.212 | |
| t | max=nominal size | 1.2 | 1.8 | 2.3 | 2.5 | 3.5 | 4.4 | 4.6 | 4.8 | 5.3 | 5.9 | 10.3 |
| min | 0.95 | 1.55 | 2.05 | 2.25 | 3.2 | 4.1 | 4.3 | 4.5 | 5 | 5.6 | 9.87 | |
| Weight of per 1000 steel products(≈kg) | - | - | - | - | - | - | - | - | - | - | - | |
| Length of Thread b | - | - | - | - | - | - | - | - | - | - | - | |
Hebei Duojia Metal Products Co., Ltd. was formerly known as Yonghong Expansion Screw Factory. It has over 25 years of professional experience in manufacturing fasteners. The factory is located in the China Standard Room Industrial Base - Yongnan District, Handan City. It conducts online and offline production and manufacturing of fasteners as well as one-stop sales service business.
The factory covers an area of over 5,000 square meters, and the warehouse covers an area of over 2,000 square meters. In 2022, the company carried out industrial upgrading, standardized the production order of the factory, improved the storage capacity, enhanced safety production capacity, and implemented environmental protection measures. The factory has achieved a preliminary green and environmentally friendly production environment.
The company has cold pressing machines, stamping machines, tapping machines, threading machines, forming machines, spring machines, crimping machines, and welding robots. Its main products are a series of expansion screws known as "wall climbers".
It also produces special-shaped hook products such as wood tooth welding sheep eye ring screws and machine tooth sheep eye ring bolts. In addition, the company has expanded new product types from the end of 2024. It focuses on pre-buried products for the construction industry.
The company has a professional sales team and a professional follow-up team to safeguard your products. The company guarantees the quality of the products it offers and can conduct inspections on the grades. If there are any problems, the company can provide professional after-sales service.
Our export countries include Russia, South Korea, Britain, France, Germany, Italy, Canada, Mexico,Brazil, Argentina, Chile, Australia, Indonesia, Thailand, Singapore, Saudi Arabia, Syria, Egypt, Tanzania.Kenya and other countries. Our products will be spread all over the world!
WHY CHOOSE US?
1.As a factory-direct upplier,we eliminate middleman margis to offer you the most competitive pricing for high-quality fasteners.
2.our factory pass the ISO 9001 and AAA certification .we have the hardness testing and the test of zinc coating thickness for galvanized products.
3.with full contrl over production and logistic,we guarantee on-time delivery even for urgnt orders .
4.our engineering team can customize faseners from prototype to mass production , including unique thread designs and anti-corrosion coatings.
5.From carbon steel hex bolts to high-tensile anchor bolts ,we provide a one-stop solution for all your fastener needs.
6.If any defect is found ,we’ll reship replacements within 3weeks of our cost .
