Nanjing Feilong Fastener manufacturing Co., Ltd. provides a full range of GB, DIN, and ISO hexagonal and flange bolts according to the "Bolt standard,” with specifications from M6 to M30 and strength grades from 8.8 to 12.9. A "Bolt Torque" recommendation table is included with the shipment, allowing users to directly look up the corresponding torque by grade and diameter without further calculation. On-site tightening can meet safety requirements in one go.

China·Nanjing Feilong Fastener Manufacturing Co., LTD

Specialized in customized Fasteners,meet your every needs.

We are major in customized fasteners With a 4,000-square-metre factory and professional production and service teams for more than 26 years, Our mission is to provide complementary services to Fastener manufacturers around the world.

Telephone: +86-25-86502859 +86-13405861131

Address: No. 6, Fengyuan Road, Xiongzhou Sub-district, Liuhe District, Nanjing City, Jiangsu Province

In the vast landscape of manufacturing and engineering, few components are as ubiquitous yet underappreciated as bolts. These small, threaded fasteners are the silent workhorses that hold together everything from skyscrapers to smartphones, from jet engines to kitchen appliances. Without them, the complex structures and machines that define modern life would simply fall apart. This article explores the world of bolts—their types, manufacturing processes, quality standards, diverse applications, and the innovations shaPing their future.  

At its core, a bolt is a type of fastener designed to join two or more parts together by passing through pre-drilled holes in the parts and securing with a nut. Unlike Screws, which typically thread directly into a material (like wood or metal), bolts require a nut to create a clamping force. The basic structure of a bolt includes a head (for applying torque), a shank (the unthreaded part), and a threaded section (where the nut screws on). The head can come in various shapes, each tailored to specific tools and applications—hexagonal (most common, used with wrenches), square (for higher torque), round (carriage bolts), and more.  

Bolts are not one-size-fits-all; they come in hundreds of types, each designed for a specific purpose. Let’s look at some of the most widely used varieties:  

Hex head bolts: The most common type, featuring a six-sided head. Used in construction, machinery, and automotive applications where high torque is needed. They are available in both partially threaded (for joining thick materials) and fully threaded (for maximum grip) versions.  

Carriage Bolts: Have a smooth, rounded head with a square neck beneath it. The square neck prevents the bolt from turning when tightening the nut, making them ideal for wood-to-wood or wood-to-metal connections (e.g., outdoor furniture, decking).  

Eye Bolts: Feature a loop (eye) at one end instead of a head. Used for lifting heavy objects or attaching cables/ropes—common in construction, marine, and industrial settings. They must be installed correctly to avoid failure under load.  

Lag Bolts: Also known as lag screws, these are heavy-duty bolts with coarse threads designed to screw directly into wood. They do not require a nut and are used for structural wood connections (e.g., framing, log homes).  

anchor bolts: Used to attach objects or structures to concrete. Types include wedge anchors (for heavy loads), sleeve anchors (versatile for concrete, brick, or block), and epoxy anchors (for high-strength, permanent connections in critical applications like bridge abutments).  

High-strength bolts: Made from alloy steels and heat-treated to achieve superior tensile strength (usually above 800 MPa). Used in structural engineering—like connecting steel beams in skyscrapers or bridge trusses—where failure could lead to catastrophic consequences.  

Creating a high-quality bolt is a multi-step process that requires precision and adherence to strict standards. Let’s walk through the key stages:  

1. Raw Material Selection: The choice of material depends on the bolt’s intended use. Common materials include:  

Carbon Steel: The most widely used (e.g., ASTM A307, SAE Grade 2 for general purpose; Grade 5 and 8 for high strength).  

Stainless Steel: Resistant to corrosion—used in food processing, marine, and medical applications (grades 304, 316).  

Alloy Steel: For high-strength bolts (e.g., chromium-molybdenum steel for automotive and aerospace).  

Non-Ferrous Metals: Aluminum (lightweight, used in aerospace and electronics) and titanium (high strength-to-weight ratio, ideal for aerospace).  

2. Cold Heading: The first step in shaping the bolt. Raw material (in the form of wire rods) is cut to length, then fed into a cold Heading Machine. The machine uses high pressure to form the bolt head from the wire—this process is efficient and improves the material’s strength by work hardening.  

3. Threading: After heading, the bolt’s shank is threaded. Two main methods are used:  

Roll Threading: The most common method for mass production. The bolt is rolled between two dies that press the threads into the shank. This process preserves the material’s grain structure, resulting in stronger threads than cut threading.  

Cut Threading: Used for custom or low-volume bolts. Threads are cut into the shank using a lathe or tapping machine—this removes material, so threads are slightly weaker than rolled ones.  

4. Heat Treatment: To enhance the bolt’s mechanical properties (strength, hardness, ductility). The process involves heating the bolt to a specific temperature, holding it, then cooling it at a controlled rate. For high-strength bolts, quenching (cooling in water or oil) and tempering (reheating to reduce brittleness) are standard.  

5. Surface Finishing: This step protects the bolt from corrosion and improves its appearance. Common finishes include:  

Zinc Plating: A thin layer of zinc is applied to the bolt—affordable and effective for general corrosion resistance.  

Hot-Dip Galvanizing: The bolt is dipped into molten zinc, creating a thicker coating—ideal for outdoor applications like construction or marine use.  

Passivation: For Stainless steel bolts—removes free iron from the surface to enhance corrosion resistance.  

Phosphating: Creates a porous layer that improves paint adhesion or lubricity (used in automotive bolts).  

6. Quality Inspection: Every batch of bolts undergoes rigorous testing to ensure compliance with standards. Tests include:  

Tensile Strength Test: Measures the maximum force the bolt can withstand before breaking.  

Hardness Test: Uses a Rockwell or Brinell tester to check the bolt’s hardness (critical for high-strength applications).  

Torque Test: Evaluates the bolt’s ability to hold torque without stripping threads.  

Corrosion Resistance Test: Salt spray tests (ASTM B117) to check how well the finish resists rust.  

Dimensional Inspection: Uses calipers, micrometers, or coordinate measuring machines (CMM) to verify that the bolt meets size and tolerance requirements.  

Bolts are everywhere—let’s explore their role in key sectors:  

In construction, bolts are essential for joining structural elements. High-strength bolts are used to connect steel beams and columns in skyscrapers like the Burj Khalifa. Anchor bolts secure steel frames to concrete foundations, ensuring stability during earthquakes or strong winds. Carriage bolts are used in wooden structures like decks and fences, while lag bolts hold heavy timber together.  

The automotive industry relies heavily on bolts. Every car has thousands of bolts—from the engine’s cylinder head (which uses torque-to-yield bolts that stretch to create a permanent seal) to the chassis and wheel hubs. Automotive bolts must withstand extreme temperatures, vibration, and stress. For example, wheel bolts must be tightened to a specific torque to prevent wheels from coming loose while driving.  

Aerospace bolts are the epitome of precision and quality. They are made from lightweight, high-strength materials like titanium or nickel-based superalloys. These bolts are used in aircraft fuselages, wings, and engines—where even a tiny defect can have fatal consequences. Aerospace bolts must meet strict standards like ASME B18.2.1 and undergo 100% inspection (including X-ray and ultrasonic testing) to detect internal flaws.  

Bolts play a crucial role in renewable energy infrastructure. Wind turbines use thousands of high-strength bolts to connect tower sections, attach blades to the hub, and secure the nacelle (the housing for the turbine’s generator). These bolts must withstand strong winds and constant vibration. Solar panel mounting systems use stainless steel bolts to attach panels to roofs or ground racks—resistant to corrosion from rain and UV rays.  

Industrial machinery (like pumps, compressors, and conveyor belts) uses bolts to hold moving parts together. Heavy equipment (excavators, bulldozers) requires bolts that can handle extreme loads and harsh environments. For example, excavator bucket pins are secured with large, high-strength bolts that must resist wear and tear from digging.  

Bolts may seem like simple components, but they are the backbone of modern industry. From the tallest skyscrapers to the smallest electronic devices, bolts play a critical role in keeping our world together. The manufacturing process of bolts is a testament to human ingenuity—combining precision engineering, strict quality control, and innovative technology to create components that are both strong and reliable. As industries evolve, so too will bolts—with smart, eco-friendly, and 3D printed bolts leading the way into the future. The next time you look at a building, a car, or a wind turbine, take a moment to appreciate the unsung heroes that hold it all together: bolts.