Coach Bolts

Coach bolts, also known as carriage bolts, are round-head, square-neck fasteners designed to securely join wood or metal components. The domed head sits flush against the material surface, while the square neck beneath bites into the substrate and prevents the bolt from rotating during installation. Tightening requires only a single spanner: a nut applied from the opposite side draws the joined materials firmly together.

Carriage bolts are commonly associated with timber applications but perform equally well in metal-to-timber and metal-to-metal connections, making them a versatile fastener across construction, joinery, and engineering.

RS is a trusted supplier and distributor of coach bolts in New Zealand, offering a broad range of sizes, materials, and finishes to suit both standard builds and demanding industrial applications.

How Do Coach Bolts Work?

When inserted into a pre-drilled hole, the square section beneath the head bites into the surrounding material, typically timber, locking the bolt in position and preventing it from rotating.

A nut threaded onto the exposed end is tightened from one side, drawing the joined components firmly together. No secondary tool is needed to hold the bolt during tightening, making installation straightforward even in confined spaces.

For correct installation, select a pre-drilled hole diameter that matches the bolt shank. Fitting a washer under the nut distributes the clamping load and protects the surface. Tighten to the torque specification appropriate for the bolt size and grade.

Types of Coach Bolts & Carriage Bolts

Coach bolts and carriage bolts are available in a range of material and finish options at RS. Selecting the right type depends on the application environment, load requirements, and exposure to moisture or corrosion.

Mild Steel Coach Bolts

Mild steel coach bolts are a cost-effective choice for indoor and sheltered fastening applications. The material provides adequate tensile strength for general construction, joinery, and furniture assembly where corrosion resistance is not a primary concern.

Stainless Steel Coach Bolts

Stainless steel coach bolts deliver strong corrosion resistance, making them the preferred choice for outdoor, coastal, and high-humidity environments. Grade 316 stainless steel suits marine and industrial settings where salt air and moisture are ongoing factors. Stainless steel carriage bolts are also compatible with treated timber, which can accelerate corrosion in mild steel fasteners over time.

Galvanised Coach Bolts

Galvanised coach bolts are coated with zinc through a hot-dip process, providing robust protection against rust and corrosion. The zinc coating suits outdoor structural applications including fencing, decking, and landscaping builds subject to regular weather exposure.

ZInc-Plated Coach Bolts

Zinc-plated coach bolts carry a thinner protective coating than galvanised alternatives, offering moderate corrosion resistance at a lower cost. Best suited to indoor or semi-sheltered applications where occasional moisture exposure is expected but prolonged outdoor weathering is not a factor.

Key Benefits of Coach Bolts

Coach bolts offer a dependable fastening solution across construction, joinery, and engineering. Key advantages include:

• Anti-Rotation Square Neck: The square section beneath the domed head locks into the substrate on installation, preventing the bolt from spinning. Tightening requires only a single spanner applied to the nut.
• Load-Bearing Strength: Coach bolts deliver strong, stable connections suited to structural and heavy-duty applications. The clamping force is distributed evenly across the joint, maintaining integrity under sustained load.
• Versatile Material Compatibility: Coach bolts perform reliably in wood-to-wood and metal-to-wood connections. The round-head profile sits flush against the surface without sinking or splitting the substrate.
• Corrosion-Resistant Options: Stainless steel and galvanised coach bolts resist moisture, weathering, and chemical exposure. Both options suit outdoor structures and environments common across New Zealand's construction and infrastructure projects.
• Straightforward Installation: No secondary tool is required to hold the bolt during tightening, simplifying installation in confined or single-access situations.

How to Choose the Right Coach Bolt

Selecting the correct coach bolt comes down to matching the fastener to your material, environment, and load requirements. Consider the following factors before specifying or purchasing:

• Material Type: Stainless steel coach bolts resist corrosion in outdoor, coastal, and humid conditions. Mild steel coach bolts suit cost-effective indoor applications where prolonged moisture exposure is not a factor.
• Finish and Coating: Galvanised coach bolts provide robust weather protection for outdoor structural applications. Zinc-plated options offer moderate protection at a lower price point, suited to semi-sheltered builds.
• Bolt Size and Length: Match bolt length to the combined thickness of the materials being joined, ensuring sufficient thread engagement for the nut. Larger diameters carry higher load ratings and suit heavier structural connections.
• Thread Size and Pitch: Confirm the thread specification is compatible with the corresponding nut. Common metric sizes range from M6 to M20; verify pitch and thread standard before ordering.
• Standards and Grade: Specifying coach bolts manufactured to DIN 603 or equivalent ensures dimensional consistency and load performance across applications.
• Pre-Drilled Hole Diameter: Match the hole diameter to the bolt shank so the square neck seats correctly into the material. An oversized hole allows the bolt to spin freely, reducing grip and compromising the joint.
• Application Type: Structural timber joints, metal-to-timber fixing, and heavy-duty outdoor structures each place different demands on the fastener. Concrete coach bolts are available where anchoring into masonry or blockwork is required.

Industrial Applications of Coach Bolts

Coach bolts and carriage bolts are used across New Zealand in construction, joinery, and engineering wherever a strong, stable, tamper-resistant fixing is required:

• Timber Construction: Coach bolts join structural beams, posts, and frames in residential and commercial builds. The domed head profile sits flush against the timber surface while the square neck maintains grip under sustained load.
• Furniture and Joinery: Carriage bolts are well suited to the assembly of heavy-duty furniture, shelving units, and cabinetry. The clean, rounded head provides an unobtrusive finish for visible fixings where appearance matters alongside strength.
• Metal-to-Timber Fixing: Coach bolts provide reliable connections between metal brackets, support plates, and timber elements. Periodically checking bolt tension ensures grip is maintained in dynamic or load-bearing assemblies over time.
• Outdoor Structures: Galvanised and stainless steel options suit decking, fencing, pergolas, and landscaping installations across New Zealand's varied climates. Corrosion-resistant finishes support long-term structural integrity in exposed environments.
• Industrial and Engineering Frameworks: Coach screw bolts feature in machinery bases, equipment frames, and structural steelwork across manufacturing and engineering environments. Single-sided tightening suits assemblies where access to the reverse face is restricted.
• General Construction: Coach bolts deliver stable, tamper-resistant connections in structural builds, including wall plates, staircase stringers, and load-bearing timber junctions.

Buy Coach Bolts Online from RS

RS New Zealand is a trusted supplier and distributor of coach bolts and carriage bolts in New Zealand, stocking a wide range of sizes, materials, and finishes to suit applications across construction, joinery, and engineering. The range includesRS PRO coach bolts, delivering consistent performance across standard and heavy-duty builds.

Beyond coach bolts, RS stocks a comprehensive range ofscrews and bolts, includingcoach screws,hex bolts, andself-drilling screws, covering a broad range of fastening requirements across construction and engineering projects.

Browse the full range online and order for delivery across New Zealand. For details on delivery timeframes and charges, visit our Delivery page.