ASME B18.5 Round Head Square Neck Carriage Bolt Carbon Steel

When sourcing fasteners for timber, fencing and light structural builds in North America, ASME B18.5 Round Head Square Neck Carriage Bolt Carbon Steel is one of the most frequently specified components. Builders prefer it for its neat hidden round head and anti-rotation square shoulder, solving the common hassle of spinning bolts during on-site assembly. For outdoor and indoor light structural projects where exposed bolt heads may cause snags or safety risks, this carriage bolt delivers a clean, reliable connection that standard hex head fasteners cannot easily match.

What Makes This Carriage Bolt Stand Out

Instead of hex heads that stick out and catch on materials, this bolt uses a smooth domed round head. The built-in square neck locks inside pre-drilled holes. Once seated, the bolt stays stationary as technicians tighten the mating UNC nut.

- No sharp protruding edges to avoid snags or injury, creating a smooth finished surface

- Square neck anti-twist design for faster field installation, eliminating extra clamping tools

- Carbon steel base delivers solid tensile strength for light structural loads

- Multiple coating options to fit indoor and dry environment projects, balancing cost and corrosion resistance

Product Spec Overview

Finish Selection Guide

Each surface treatment brings different performance and cost benefits. Pick coating based on your project environment, budget and expected service life.

Key Benefits of Using ASME B18.5 Standard

Choosing fasteners manufactured strictly to ASME B18.5 ensures interchangeability with existing North American assemblies. Every dimensional feature, including head diameter, square neck size and UNC thread profile, follows unified industry specifications. This consistency removes compatibility risks when replacing old fasteners or assembling new structures, a critical factor for contractors managing multiple project sites.

We strictly screen all incoming steel raw materials to guarantee each batch meets the carbon steel grade requirements before forging work begins.

Typical Project Applications

North American fabricators, fence contractors and agricultural equipment manufacturers rely on this carriage bolt. It works perfectly for fence panels, timber frame joints, trailer body assembly and farm machinery frames. The flush rounded head keeps exposed surfaces smooth and safe. It is also widely used in playground framework, warehouse rack accessories and custom metalwork projects where protruding fastener heads are undesirable.

Our Manufacturing & Batch Inspection

Raw carbon steel rods are hot forged to shape the round head and square neck, then thread rolled for precise UNC threads. Hot forging optimizes the grain structure of the steel, improving the bolt’s tensile strength and resistance to shear force. Every production batch goes through random sampling for dimension check, thread fit and coating inspection. Full batch traceability records are kept for quality audits and component tracking.

Custom & Order Support

We accept trial small orders as well as volume bulk shipments. Custom length and marking options are available subject to MOQ. Our technical team can help match compatible UNC nuts for your assembly design, and provide professional advice on coating selection according to your working environment. We support customized packing solutions for special project requirements.

Packaging for Export Shipment

Products are packed in export cartons with rust-proof inner protection. Custom shipping marks and product labels can be printed according to your requirements. Each carton will be carefully sealed to prevent damage during long-distance sea or land transit. Complete export documentation will be prepared for smooth customs clearance.

Quick Customer Questions

Q: Why choose carriage bolt over regular hex bolt?

A: Its round head sits flush, and square neck prevents bolt spinning when tightening nuts. Great for exposed surfaces.

Q: What nuts fit this ASME B18.5 carriage bolt?

A: Standard UNC hex nuts or ASME B18.2.2 heavy hex nuts are compatible.

Q: Can I request samples?

A: Samples are available. Buyers only need to cover the freight cost.