5/16 Black Carriage Bolt

The 5/16 Black Carriage Bolt, with a nominal diameter of approximately 8mm, is a widely used "golden size" standard fastener.  It achieves a precise balance between connection strength and adaptability, combining practical performance with a uniform aesthetic. It is a core connecting component in wood structure connections, agricultural equipment assembly, and industrial maintenance scenarios.

As a source factory with over 15 years of experience in fastener research, development, and manufacturing, we have a deep understanding of the market demand and application challenges of various standard fasteners. Our 5/16 black carriage bolts are manufactured in strict accordance with both DIN 603 (German standard) and GB/T 14 (Chinese national standard), using high-quality carbon steel base material and a professional black surface treatment process. This black coating not only gives the bolt a low-profile and uniform appearance but also effectively isolates it from the air, providing basic rust and corrosion protection, making it suitable for long-term use in multiple scenarios.

Core Product Advantages

1. Precise 5/16-inch specifications, maximum versatility

The 5/16-inch specification is an ideal choice for light to medium-duty structural connections. It offers superior strength compared to smaller screws and greater flexibility than larger bolts, adapting to most standard drill hole sizes. We precisely calibrate the bolt dimensions, strictly controlling everything from thread accuracy to head size, ensuring perfect compatibility with standard 5/16-inch nuts and washers on the market, guaranteeing a smooth connection process and stable and reliable subsequent use.

2. Professional black surface treatment, combining protection and aesthetics

Our black surface treatment mainly uses two mature processes: black oxide and black paint, matched to different application needs:

Black oxide process: Forms a dense oxide film on the bolt surface, improving surface smoothness, reducing friction during use, and providing basic rust protection, while also offering some heat treatment protection;

Black paint process: The coating is thicker, providing better isolation from moisture and oxygen, superior rust resistance compared to the ordinary black oxide process, and is more cost-effective, offering excellent value for money. Furthermore, the uniform black appearance is understated and professional, blending seamlessly with dark wood or industrial equipment without disrupting the visual harmony of the scene, making it particularly suitable for assembly scenarios with specific aesthetic requirements.

3. Classic Square Neck Anti-Loosening Design for Efficient and Hassle-Free Installation

The square neck design is a core advantage of carriage bolts and a key aspect of our quality control process. The square neck below the bolt head, when inserted into the workpiece hole, securely locks against the hole wall, creating a reliable self-locking effect. When tightening the nut, the bolt body does not rotate, eliminating the need for additional fixing of the bolt on the other side. Installation can be completed with just one wrench. This single-sided operation significantly improves construction efficiency and reduces labor costs in scenarios involving working at heights, confined spaces, or situations where only one side is accessible.

Core Technical Parameters

Typical Application Scenarios

With years of industry service experience, our 5/16 Black Carriage Bolt has been widely used in various fields, adapting to the actual needs of different scenarios:

1. Wooden Structures and Furniture: Commonly used for connecting and fixing solid wood frames, floor joists, and furniture legs. The black bolt head complements dark wood, ensuring both secure connections and enhanced overall aesthetics;

2. Agriculture and Animal Husbandry: Suitable for applications such as pasture fences, livestock sheds, and feed trough assembly. The square neck anti-loosening design effectively resists impacts and pulling from livestock, and the black coating can withstand humid outdoor environments, providing basic moisture and corrosion protection;

3. Industrial Maintenance and Equipment: Used for fixing factory machine guards, assembling conveyor belt supports, and installing maintenance panels. The black appearance is dirt-resistant and easy to clean, adapting to general oil and humidity in factory environments, ensuring a longer service life;

4. Home Improvement and DIY: Suitable for home stair railing installation, outdoor patio construction, and storage rack assembly. Easy to install without special tools, making it a practical helper for DIY enthusiasts.

Company Strength and Quality Assurance

We are Ningbo Gangtong Zheli Fasteners Co., Ltd., established in 2001.  We have developed a mature system for fastener research, development, production, and sales. The factory covers an area of 15,000 square meters, with a stable monthly production capacity of 2,000 tons and annual sales exceeding US$15 million. The company is equipped with a complete R&D team, a full-chain supply chain management system, and large-scale warehousing facilities. We specialize in the production of high-strength standard fasteners and can provide integrated MRO procurement and distribution services for metal fasteners, fully meeting customer procurement needs. Quality is the core lifeline of fasteners, and we control product quality throughout the entire process: In the raw material stage, we strictly select high-quality carbon steel, and each batch of raw materials undergoes chemical composition spectral analysis to ensure that the material meets the standards; in the production stage, we use advanced cold heading and roll threading processes to ensure continuous and complete metal flow lines, improving the overall strength of the product. At the same time, we control the size of the square neck through precision molds to ensure stable anti-loosening effect; in the finished product testing stage, we fully implement the ISO 9001 quality management system, and conduct hardness tests, salt spray tests (to verify rust resistance), and tensile tests on each batch of finished products to ensure stable and reliable product performance. Material certificates (Mill Test Certificates) can be provided according to customer requirements, enabling full traceability of quality.

Our product range is extensive, covering heavy-duty hexagonal bolts, heavy-duty hexagonal nuts, threaded rods, studs, washers, screws, etc., with materials including carbon steel, alloy steel, and stainless steel. We strictly adhere to international standards such as DIN, ISO, EN, JIS, ASTM/ANSI/ASME/SAE, BS, and AS. Our products are exported to North America, Europe, Australia, Southeast Asia, the Middle East, Latin America, and many other regions, and are suitable for various fields such as building steel structures, bridges, oil pipelines, mechanical equipment, furniture, ships, and railways.

Reasons to Choose Us

1. Direct supply from the source factory, more competitive costs: As a physical manufacturer in the core fastener production area of China, we have a complete production line from raw material procurement to finished product delivery, eliminating all intermediate links and directly providing customers with highly competitive ex-factory prices. We have sufficient stock of standard specifications and can quickly respond to delivery needs;

2. Professional technical team, high response efficiency: Our company's engineering team has rich industry experience and can accurately complete non-standard customization (OEM/ODM) services based on drawings or samples provided by customers; we can quickly respond to and provide solutions for technical problems encountered by customers during use;

3. Global service experience, more worry-free cooperation: With many years of experience in the international market, we have established a complete logistics and distribution system and after-sales service system, which can accurately match the standard requirements and market needs of different regions. We are committed to establishing long-term and stable cooperative relationships with our customers, ensuring smooth procurement, distribution, and after-sales processes.