Product Category
Product Overview
A carriage bolt — also commonly referred to as a coach bolt, cup head bolt, or round head square neck bolt — is a specialized fastener designed for secure, tamper-resistant connections where access is limited to one side. Unlike standard hex bolts that require a wrench on both ends, the carriage bolt’s square neck beneath the domed head locks into the material (typically wood or soft metal) when the nut is tightened, preventing the bolt from rotating and enabling single-wrench installation.
This self-locking design makes carriage bolts an essential fastening solution across multiple industries — from heavy timber construction and outdoor decking to automotive trailer assembly and marine infrastructure.
Key Features & Benefits
Feature | Benefit |
|---|---|
Smooth domed head | Provides a clean, snag-free finished appearance; reduces injury risk on playgrounds and high-traffic areas |
Square neck under head | Self-locking design eliminates need for a second tool; prevents rotation during nut tightening |
Partial or fully threaded shank | Available in both configurations to suit different material thicknesses and clamping requirements |
One-sided installation | Allows fastening in tight spaces where only the nut side is accessible |
Multiple material grades | Carbon steel for high strength; stainless steel for corrosion resistance; alloy steel for extreme loads |
Variety of surface finishes | Zinc plated, hot dipped galvanized, black oxide, Geomet — matched to environmental exposure |
Materials, Grades & Finishes — Complete Specification
Selecting the right material and finish is critical for performance and longevity in your specific application. Below is a comprehensive breakdown:
Carbon Steel Carriage Bolts
Grades: Class 4.8, 5.8, 8.8, 10.9, 12.9; ASTM A307 Grade A; SAE J429 Grade 2, Grade 5, Grade 8
Properties: High tensile strength, excellent load-bearing capacity, cost-effective for heavy-duty applications
Limitation: Prone to corrosion without protective coating
Applications: Structural framing, machinery mounting, construction, heavy equipment
Stainless Steel Carriage Bolts
Grades: A2-70 (SS304), A4-80 (SS316)
Properties: Exceptional rust and corrosion resistance, low maintenance, long service life in harsh environments
Limitation: Higher cost than carbon steel; lower tensile strength than some alloy steels
Applications: Marine decks, docks, piers, boat building, coastal structures, outdoor fixtures, food processing equipment
Zinc Plated Carriage Bolts
Finish: Clear zinc, yellow zinc, blue zinc, black zinc
Properties: Good corrosion resistance for moderate outdoor conditions; cost-effective alternative to stainless
Limitation: Coating can wear over time; less durable than HDG or stainless in extreme environments
Applications: General construction, furniture assembly, indoor industrial use, moderate outdoor exposure
Hot Dipped Galvanized (HDG) Carriage Bolts
Properties: Thick zinc coating provides high corrosion resistance; excellent for outdoor, wet, and coastal applications
Applications: Outdoor structures, utility poles, agricultural equipment, fencing, docks
Black Oxide Carriage Bolts
Properties: Mild corrosion resistance; sleek, non-reflective appearance; minimal dimensional change
Limitation: Not suitable for outdoor or wet environments; limited rust protection without oiling
Applications: Furniture assembly, indoor machinery, automotive trim, decorative hardware
Applications — Industry Use Cases
Industry | Specific Applications |
|---|---|
Wood Construction | Decks, fences, pergolas, playgrounds, timber framing — the smooth head provides a snag-free finish |
Metal-to-Wood Fastening | Attaching metal brackets, plates, or hardware to wooden beams, furniture frames, support structures |
Automotive & Trailers | Truck beds, trailer wood floors, stake sides, tie-downs, off-road vehicles — vibration resistance is key |
Marine & Dock Construction | Docks, piers, boat building, coastal structures — stainless steel or HDG required |
Furniture Manufacturing | Holding wooden components together without protruding screw heads — aesthetic and durable |
Agricultural Equipment | Farm machinery, fencing, heavy-load connections — grade 5 or 8 for strength |
Signage & Street Fixtures | Street signs, light poles, outdoor fixtures — tamper-resistant fastening |
Playground & Park Equipment | Snag-free head prevents injuries while ensuring secure hold |
Sourcing & Export Information
Packaging: Bulk in cartons (25kg max) + wooden pallets; or customized per customer requirements
Lead Time: 20–30 days based on order quantity
Quality Assurance: ISO 9001:2015 certified manufacturing; dimensional inspection, raw material verification, hardness testing
Export Markets: North America, Europe, Australia, Southeast Asia, Middle East, South America
Why Choose Our Carriage Bolts?
Full standard compliance — Manufactured to DIN 603, ISO 8677, ASME B18.5, ASTM A307, JIS B 1171, and BS 4933 standards
Wide size range — Metric M5–M24; Imperial #10–1″; lengths from 16mm to 300mm (0.5″ to 12″)
Multiple material options — Carbon steel, stainless steel (SS304/SS316), alloy steel
Flexible surface treatments — Zinc plated (clear/yellow/blue/black), hot dipped galvanized, black oxide, Geomet
Bulk supply capability — Competitive pricing for OEM, contractor, and distributor volumes
Quality assured — Rigorous in-process and finished product inspection
