Carriage Bolts Manufacturer
MT.BOLTS manufactures Carriage Bolts, which are externally threaded fasteners with a round, smooth head and a square neck directly beneath it. The square section resists turning once installed in a square hole or wood, allowing the bolt to be tightened from the nut side only. These bolts are commonly used in wood-to-wood and wood-to-metal applications, offering a clean, tamper-resistant finish ideal for structural, decorative, and security uses. MT.BOLTS supplies high-performance carriage bolts in a variety of materials, dimensions, and standards to meet a wide range of construction and engineering demands.
- System of Measurement:
Metric (M6–M20) | Imperial (1/4″ to 1″) - Length Range:
20 mm to 300 mm | 0.75″ to 12″ - Thread Pitch:
Metric (Coarse) | UNC - Thread Type:
Partially threaded (standard for carriage bolts) - Head Type:
Round head with square neck - Finish Options:
Plain, zinc-plated, hot-dip galvanized, black oxide, passivated, or custom coatings - Standards:
- ASME B18.5 (Round Head Square Neck Bolts)
- DIN 603 (Metric Carriage Bolts)
- ISO 8677
Carriage Bolts Material Types
MT.BOLTS supplies carbon steel, stainless steel, duplex steel, and nickel-based alloy Carriage Bolts, meeting the demanding requirements of chemical, marine, and high-temperature environments, compliant with various international standards.
| Material Category | Common Grades/Models | Description |
| Carbon Steel | ASTM A307, A325, A490 | High strength and cost-effective, suitable for general structures; requires anti-corrosion coating. |
| Stainless Steel | 304 (A2), 316 (A4), 321, 410 | Excellent corrosion resistance; widely used in food, chemical, and construction industries |
| Duplex Stainless Steel | UNS S31803/S32205 (F51), UNS S32750 (F53) | High strength with superior chloride corrosion resistance; used in seawater, petrochemical, and paper industries |
| Monel Alloys | Monel 400, Monel K500 | Excellent seawater corrosion resistance and mechanical strength; used in marine engineering and pump systems |
| Hastelloy Alloys | Hastelloy C276, C22, B2, X | Excellent resistance to strong acids and oxidizing media; widely used in chemical equipment and flue gas desulfurization |
| Inconel Alloys | Inconel 600, 625, 718 | Resistant to high temperature, pressure, and corrosion; used in heat exchangers, aerospace, and nuclear industries |
| Incoloy Alloys | Incoloy 800, 825, 925 | Ideal for high-temperature acidic environments; widely used in petroleum refining and heat treating systems |
| Nickel Alloys | Nickel 200, 201 | Pure or high-nickel alloys with excellent conductivity and alkali resistance; used in electronics and chemical applications |
Carriage Bolts System of Measurement
- Metric Sizes: M6 to M20
- Imperial Sizes: 1/4″ to 1″
- Length Range:
- Metric: 20 mm to 300 mm
- Imperial: 0.75″ to 12″
- Thread Pitch: Metric (Coarse) | UNC
- Thread Type: Typically partially threaded for structural grip
Carriage Bolts Common Standards
- ASME B18.5 – Round Head Square Neck Bolts
- DIN 603 – Metric Carriage Bolts
- ISO 8677 – International standard for round head bolts with square neck
Carriage Bolts Surface Finishes
- Zinc-plated – Corrosion resistance in indoor environments
- Hot-dip galvanized – Excellent protection in outdoor/marine use
- Black oxide – Mild corrosion resistance, often for aesthetic or indoor use
- Passivated – Used on stainless steel bolts to improve corrosion resistance
- Custom Coatings (e.g., PTFE) – Non-stick, chemical-resistant for harsh environments
Why Choose MT.BOLTS
- Material Diversity
- Standardized Production
- Ample Inventory
- Competitive Pricing
- Low-MOQ Customization
Benefits and Limitations of Carriage Bolts
Advantages
- Tamper-resistant from the head side (no tool access)
- Smooth, rounded head ideal for visible or safety-sensitive applications
- Square neck prevents rotation during tightening
- Widely used in wood structures and furniture assembly
Disadvantages
- Not suitable for metal-only assemblies unless square holes are used
- Requires access to the nut side for installation
- Limited head-driving options (cannot be driven from the head side)
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Carriage Bolts Applications
- Wood-to-wood and wood-to-metal connections
- Fencing, decking, and timber structures
- Playground equipment
- Architectural assemblies requiring smooth finishes
- Furniture and cabinetry
FAQ About Carriage Bolts
Yes, but a square hole must be used to prevent bolt rotation, or an auxiliary locking method is needed.
Typically, carriage bolts are partially threaded to ensure shear strength in the unthreaded section.
Yes, if not damaged during removal, but threads and neck fit should be checked before reuse.
Installation requires a wrench or socket for the nut; the bolt head is held by the square neck during tightening.
Stainless steel offers high corrosion resistance, especially grades like 304 or 316, making them ideal for outdoor or marine use.
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