Carbon steel carriage bolt, also known as coach bolt (round head square neck bolt), is widely used for fastening wood-to-wood, wood-to-metal, and certain metal-to-metal connections where a smooth finished head is required. The square neck under the round head embeds into the material during tightening, preventing rotation and ensuring stable installation without damaging the exposed surface. It is commonly applied in structural timber construction, outdoor installations, and general industrial fastening.
ZSD Screw specialize in high-strength carbon steel carriage bolts designed for structural and industrial use. By integrating in-house production processes including cold heading, precision thread rolling, heat treatment, and surface finishing with rigorous quality control inspection, ZSD Screw delivers reliable, international-standard fasteners directly to global customers, ensuring consistent dimensional accuracy, stable mechanical properties, and long-term fastening performance.
Standard carriage bolt dimensions are manufactured according to DIN, ISO and ASTM standards. Custom drawings and samples are accepted.
Type: Carriage Bolt (Round Head Square Neck Bolt)
Diameter Range: M2 – M64
Thread Type: Metric / UNC / UNF
Thread Form: Partial Thread (standard configuration under DIN 603)
Standard: DIN 603 / ISO 8677 / ASTM A307
Tolerance: According to standard or customer drawing.
We supply carriage bolts in a wide range of materials including: Carbon Steel (Q235, 35#, 45#), Alloy Steel (40Cr, SCM435), Stainless Steel (304, 316), Brass and Aluminum (on request).
Strength Grades: Carriage bolts are available in different strength grades to meet various load requirements: 4.8, 8.8, 10.9, 12.9, 14.9. ASTM grades: ASTM A307. Heat treatment is completed in-house where applicable to ensure stable mechanical properties and reliable performance.
Surface Treatment: To improve corrosion resistance and service life, we offer the following surface finishes: Zinc plated (blue / white / yellow), Black oxide, Hot dip galvanized, Zinc flake coating, Phosphate, Dacromet. Special surface treatments are available according to customer requirements.
Applications: In mechanical equipment manufacturing, ZSD Screw carbon steel carriage bolts are used in machine bases, protective guards, support brackets, equipment frames, and auxiliary structural assemblies that combine steel and non-metal materials. The square neck design helps prevent bolt rotation during tightening, supporting controlled preload and consistent fastening stability under vibration and cyclic mechanical loads.
In electronic equipment and industrial electronics, carbon steel carriage bolts are applied in equipment cabinets, enclosure panels, mounting brackets, and supporting frames where a smooth external head improves safety and surface integrity. Reliable fastening performance contributes to alignment accuracy and structural stability in control systems and industrial production lines.
In the new energy sector, carbon steel carriage bolts are used in solar mounting structures, photovoltaic support systems, and auxiliary structural connections involving metal and composite materials. Stable mechanical strength and appropriate surface treatment help maintain long-term durability under outdoor exposure, temperature variation, and wind load conditions.
In conventional and renewable power generation facilities, these bolts are applied in auxiliary equipment frames, cable support systems, platform structures, and maintenance assemblies. Secure fastening performance supports structural reliability under mechanical vibration, environmental stress, and long-term operational loading.
In the automotive and transportation industries, ZSD Screw carbon steel carriage bolts are used in vehicle body auxiliary structures, cargo compartments, trailer assemblies, and wooden or composite panel connections. Consistent dimensional accuracy and tensile performance support reliable assembly quality and operational safety under dynamic driving conditions.
In heavy industry and engineering equipment manufacturing, these bolts are widely applied in construction machinery guards, storage systems, agricultural equipment, conveyor protection components, and structural support assemblies. Applications requiring dependable clamping force and resistance to loosening under vibration benefit from controlled production processes and stable mechanical properties, helping ensure long-term structural integrity in demanding industrial environments.
