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Carriage Bolts

Stop bolt spinning. Square neck locks tight into timber.
Clean dome finish, no snag. Built for outdoor use.
Sinsun delivers certified strength from M6 to M24.
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Sinsun Carriage Bolts – Round Head Square Neck Fasteners for Timber Construction, Deck Building, and Structural Wood-to-Metal Connections

We manufacture forged carriage bolts (coach bolts / cup head bolts / round head square neck bolts) in Grade 4.8–10.9 carbon steel, A2/A4 stainless steel, and hot-dip galvanized finishes. From deck railing post connections and fence rail joints to timber frame structures, marine docks, and playground equipment, each Sinsun carriage bolt meets DIN 603, ISO 8677, and ASME B18.5 with full traceability. Request WLL-certified bulk pricing for your construction or outdoor furniture project today.

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Sinsun Carriage Bolts Factory | Stainless Steel & Galvanized Carriage Bolts

Sinsun is a professional carriage bolts factory and trusted global supplier. We manufacture standard, ribbed neck, stainless steel and galvanized carriage bolts for woodwork, fence and structural fastening. Get high-precision anti-rotation carriage bolt solutions at factory direct prices.

Sinsun Carriage Bolts | Product Overview & Core Advantages.

Sinsun Carriage Bolts Product Overview & Core Advantages

Carriage bolts, also known as round head square neck bolts or coach bolts, are specialized fasteners with a smooth domed head and an anti-rotation neck structure. In Europe, carriage bolts (for industrial clients) are called pernos de carroza, in Australia, coach bolts (common in construction). Unique neck locking prevents bolts from spinning during tightening, preventing the most common assembly problems with wood and thin metal connections.

Sinsun is a professional carriage bolt manufacturer, which creates obvious product differentiation from generic fastener suppliers. Most of the regular factories produce only regular square neck carriage bolts with a single fixed structure. We diversify neck designs, surface coatings and materials grades to meet different base materials and outdoor environments. All our carriage bolts are incadrated with ISO and DIN industrial standards to guarantee consistent thread accuracy and a secure neck lock fit.

Many global buyers suffer from recurring defects from low quality carriage bolts, including head scratching, neck slipping and poor anti-corrosion performance. Eliminating these pain points is achieved through one-time precision forging and strict layer-by-layer quality inspection. Our mainstream stainless steel carriage bolts, galvanized carriage bolts, ribbed neck and short neck carriage bolts have stable locking force under long-term vibration and outdoor exposure. We also provide non-standard size customization to meet the specific construction and furniture-making demands.

Types of Carriage Bolts | Sinsun Full Hot-Selling Classification

 Explore all popular Sinsun carriage bolts types, including standard square neck, ribbed neck, galvanized, stainless steel and short neck carriage bolts for diverse fastening needs.

Square Neck Carriage Bolts

Square Neck Carriage Bolts

Sinsun's standard square neck carriage bolt has a traditional round smooth head and square neck structure. The square neck fits snugly into pre-drilled holes to lock position and prevent rotation when the nut is tightened. Rounded Burr-Free Head Prevents Scratching of Wood and Furniture Surfaces. These universal bolts work perfectly on most general woodworking, fence and structural fastening projects.
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Galvanized Carriage Bolts

Galvanized Carriage Bolts

Our galvanized carriage bolts have electro-plated and hot dip zinc anti-rust treatments. The heavy zinc coating protects against oxidation and weather corrosion by isolating air and moisture. Hot-dip galvanized versions have a thicker protective coating for longer life in outdoor service. These cost-effective bolts are appropriate for exterior fencing, garden facilities and municipal construction projects.
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Stainless Steel Carriage Bolts

Stainless Steel Carriage Bolts

Stainless steel carriage bolts use premium 304 and 316 stainless steel raw materials, with excellent corrosion and oxidation resistance. They resist salt fog, high humidity, and chemical erosion without rusting or structural deterioration. The smooth polished head keeps a neat appearance for long-term outdoor use. These bolts are suitable for coastal, marine and humid workshop fastening applications.
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Ribbed Neck Carriage Bolts

Ribbed Neck Carriage Bolts

The ribbed neck carriage bolt has a neck with multiple ridges, rather than the usual square. Raised ribs offer better occlusion in base materials and better anti-rotation than standard types. An excellent design for thin wood composite panels and soft metal sheets. We make all ribs of equal depth so we can grip without cracking material.
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short neck carriage bolts

short neck carriage bolts

Short neck carriage bolts have compact shortened neck structures designed for small plates and slim component assembly. The shorter neck length avoids protrusion and interference when mounted on thin mounting bases. They retain full anti-rotation functions while adapting to tight installation spaces. These special bolts are extensively used in furniture splicing and thin metal frame fixing.
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Grade 5 Carriage Bolts

Grade 5 Carriage Bolts

Sinsun Grade 5 carriage bolts are professionally heat treated to increase tensile and shear strength. The upgraded carbon steel material is resistant to deformation and fracture under heavy load pressure. They have stable fastening performance under high vibration and high pressure working conditions. These industrial-strength bolts are ideal for heavy-duty structural and mechanical assembly applications.
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Long Carriage Bolts

Long Carriage Bolts

Sinsun long shank carriage bolts deliver the solution with extended overall lengths up to 300 mm (metric) or 12 inches (imperial) with either full or partial threads depending on your engagement depth. The extended shank is fully machined to the same precision tolerances as the standard sizes with the square neck geometry unchanged for proper bite into the timber. These are made from Grade 8.8 carbon steel, A2/A4 stainless steel or HDG finish.
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Heavy Duty Carriage Bolts

Heavy Duty Carriage Bolts

We offer Grade 8.8 carbon steel coach bolts with a tensile strength of 800 MPa, which are suitable for most structural timber applications under Eurocode 5. 10.9 grade increases this to 1040 MPa for large industrial projects.Generally, grades 12.9 and 12.9m (1220 MPa) are reserved for seismic zones and machinery mountings that carry very high loads. All heavy carriage bolts are quenched and tempered and the property class is clearly marked on the head. The square neck on these heavy bolts is case hardened to resist deformation when driven into dense wood.
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carriage bolt size table & technical parameters

DIN 603 Carriage Bolts — Metric Dimensions

Thread (d) Pitch (mm) Head Diameter dk max/min (mm) Head Height k max/min (mm) Neck Width f max/min (mm) Neck Height v max/min (mm) Thread Type Standard Lengths (mm)
M5 0.8 13.55 / 12.45 3.30 / 2.70 4.10 / 2.90 5.48 / 4.52 Partial thread 20–50
M6 1 16.55 / 15.45 3.88 / 3.12 4.60 / 3.40 6.48 / 5.52 Partial thread 25–60
M8 1.25 20.65 / 19.35 4.88 / 4.12 5.60 / 4.40 8.58 / 7.42 Partial thread 30–100
M10 1.5 24.65 / 23.35 5.38 / 4.65 6.60 / 5.40 10.58 / 9.42 Partial thread 30–150
M12 1.75 30.65 / 29.35 6.95 / 6.05 8.75 / 7.25 12.70 / 11.30 Partial thread 40–200
M16 2 38.80 / 37.20 8.95 / 8.05 12.90 / 11.10 16.70 / 15.30 Partial thread 60–250
M20 2.5 46.80 / 45.20 11.05 / 9.95 15.90 / 14.10 20.84 / 19.16 Partial thread 70–300

Source: DIN 603:2017‑05. Metric coarse threads per ISO 261. Custom lengths and full thread variants available upon request.

ASME B18.5 Carriage Bolts — Imperial Dimensions

Nominal Size (inch) Threads per Inch (UNC) Head Diameter (inch) Head Height (inch) Neck Width (inch) Standard Lengths (inch)
1/4″ 20 0.563 0.125 0.172 3/4 – 6
5/16″ 18 0.688 0.156 0.219 3/4 – 8
3/8″ 16 0.813 0.188 0.266 1 – 8
1/2″ 13 1.063 0.25 0.344 1 – 10
5/8″ 11 1.313 0.313 0.438 1 – 10
3/4″ 10 1.563 0.375 0.5 1 – 12
1″ 8 2.063 0.5 0.625 2 – 12

SINSUN
Sinsun Carriage Bolts Core Technical Parameters

  • Meta Description: View Sinsun carriage bolts technical parameters including materials, strength grades, surface treatments and industrial standards for reliable structural fastening.
  • Product Aliases: Coach bolts, round head square neck bolts, anti-rotation carriage fasteners.
  • Main Materials: Low carbon steel, medium carbon steel, 304/316 stainless steel.
  • Strength Grades: Grade 2 ordinary grade, Grade 5 high-strength heat-treated grade.
  • Surface Treatment: Electro-galvanized, hot-dip galvanized, black oxide, plain finish.
  • Compliant Standards: DIN 603, ISO 8677, GB/T 12-85 international manufacturing standards.
  • Structural Feature: Smooth domed head, anti-rotation neck, partial thread design.
  • Custom Service: Support custom neck height, length and special anti-corrosion coatings.

Main Applications of Sinsun Carriage Bolts

 Key applications of Sinsun carriage bolts in woodworking, fence installation, furniture manufacturing and outdoor structural fastening projects.

Woodworking & Furniture Manufacturing

1. Woodworking & Furniture Manufacturing

●Carriage bolts are the primary fasteners used to join solid wood furniture and assemble wooden parts. Surfaces are flat and safe with no sharp edges or scratches thanks to the smooth, round head.The anti-rotation neck prevents the bolt from spinning during repeated use and maintenance. Wooden structures are tightened and stabilized with these bolts to last for many years inside and outside.

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2. Fence & Guardrail Installation

●Galvanized carriage bolts are the go-to option for securing outdoor fences, guardrails and railing systems. The zinc coating resists rain and wind erosion, preventing rust failure in harsh environments. The firm neck locking structure does not loosen from external vibration and impact. They are responsible for the long term stability of boundary and safety fence structures. 

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Woodworking & Furniture Manufacturing
Outdoor & Municipal Facilities

3. Construction & Structural Engineering

● High-strength grade 5 carriage bolts support wooden building frames, steel-to-wood composite structures and temporary construction facilities. The improved material toughness can withstand large structural loads and dynamic pressures. The standard thread and neck size assure precise assembly tolerances. These bolts improve the overall safety of the structure and the efficiency of construction.
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4. Outdoor & Municipal Facilities

●The carriage bolts are made of stainless steel and hot-dip galvanized and are suitable for outdoor municipal facilities, park equipment and garden landscape projects. They are resistant to extreme weather conditions and environmental corrosion. The neat head design maintains public facilities' uniform look. The reduction of frequent replacements and the reduction of maintenance costs. 

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Construction & Structural Engineering
Composite & Thin Plate Fastening

5. Composite & Thin Plate Fastening

● Ribbed Neck & Short Neck Carriage Bolts For Thin Metal Plates, Composite Boards And Light Equipment Base Fixing. The special rib structure increases friction with soft materials to improve anti-slip performance. It is small enough to prevent structure protrusion and assembly interference. They perfectly solve the problem of loose fastening of thin and soft base materials.
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boltcarriage bolt installation & selection guide

Choosing the Right Carriage Bolt for Your Project

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Before selecting any carriage bolt, consider three factors

load type, exposure environment, and assembly access.
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Light duty (furniture, indoor joinery)

Grade 4.6 or 4.8 carbon steel, zinc plated, M6 or M8 diameter.
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Structural timber (decks, pergolas, fencing)

Grade 8.8 carbon steel minimum, M10 or M12 diameter, hot‑dip galvanized for outdoor.
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Heavy industrial / high vibration

Grade 10.9 or 12.9 carriage bolts with nyloc nuts or threadlocker.
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Marine / coastal / chemical exposure

A4-80 (316) stainless steel carriage bolts regardless of grade. No exceptions.
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Public safety (playgrounds, benches)

Stainless steel with tamper‑resistant shear nuts for vandal‑prone areas.

Environment & Finish Selection Table

Environment Recommended Carriage Bolt Recommended Nut Additional Protection
Indoor, dry (furniture, workshop) Zinc plated Grade 4.6 or 4.8 Zinc hex nut None needed
Indoor, humid (bathroom, pool house) Zinc plated or stainless A2-70 (304) Matching zinc or A2-70 Flat washer
Outdoor, general (decks, fencing) HDG carbon steel Grade 8.8 HDG nut Penny washer + flat washer
Coastal within 1 km of saltwater A4-80 (316) stainless steel A4-80 stainless nut Penny washer, anti‑seize on threads
Marine / saltwater immersion A4-80 (316) stainless steel A4-80 stainless nyloc nut Nyloc nut + penny washer
Agricultural / chemical exposure A4-80 (316) or A2-70 with coating Matching nut Threadlocker or nyloc
Public / playground / vandal‑prone A4-80 with shear nut Shear nut (breakaway) None (shear nut eliminates vandal tool access)

Global Customer Reviews | Sinsun Carriage Bolts Verified Feedback

Authentic global client reviews for Sinsun carriage bolts, covering quality stability, anti-rotation performance and factory service from construction and furniture industries.

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Klaus W. – Timber Frame Builder (Germany).
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For all our pergola beam connections, we use M12 carriage bolts. The Sinsun Grade 8.8 hot-dip galvanized bolts have uniform head dimensions and the square neck bites into hardwood without damage. No more spinning bolts when you tighten them. Reordered 3,500 pcs for our 2025 season.”
user39
Michelle T. – Decking (Australia)
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There is a need for stainless steel coach bolts on coastal Queensland decks. Other suppliers sell us A2 (304) that pits after 2 years. sinsun is selling the real A4-80 with certificates. In the past five years, nothing has corroded on our client's fasteners.“We are moving all the marine work to Sun.
User Persona46
Carlos R. – Procurement of Public Works (Brazil)
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We have 47 public playgrounds in So Paulo. Carriage bolts should be tamper resistant. Our vandalism problem has been solved by Sinsun's shear nut system with standard carriage heads. Council inspectors approve stainless material and installation is quick. “Now required for all upcoming park projects.”
User Persona50
Johan v. – Farm Equipment Fabricator (South Africa)
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“We expose our livestock handling panels to a lot of vibration - cattle bump them every day." Standard carriage bolts come loose within weeks. Sinsun Grade 10.9 carriage bolts with Nyloc nuts.Torque remains constant after six months In KwaZulu-Natal, our humid coastal climate also doesn't play well with our HDG finish .An excellent value for quality.
User Persona13
Emre Y. – Manufacturer of Garden Structures (Turkey).
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We export timber gazebos to Europe and overseas. The assembly instructions only say to tighten from one side and only carriage bolts allow for that. All Sinsun M8 and M10 necks are uniformly square in shape for all sizes. “Switching improved our customer complaint rate for loose joints by 40 percent.
User Persona8
Rajesh P.  – Owner Furniture Factory (India)
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“Our Mumbai workshop assembles 20,000 flatpack shelving units every month with M6 carriage bolts .Previously, we received bolts with poorly formed square necks - they spun in the hole.Sinsun’s square necks are clean and crisp. “Zero assembly line rejections on the last 6 shipments.”

Hot FAQ | Sinsun Carriage Bolts Common Questions

    • 1

      Q: What are carriage bolts used for?

      Carriage bolts focus on anti-rotation fastening for woodwork, fences, furniture and outdoor structural components.

    • 2

      Q: What is the advantage of ribbed neck carriage bolts?

      Ribbed necks deliver stronger anti-slip grip for thin plates and soft composite materials than square necks.

    • 3

      Q: Are galvanized carriage bolts good for outdoor use?

      Hot-dip galvanized carriage bolts provide durable anti-rust protection for long-term outdoor exposure scenarios.

    • 4

      Q: When to choose short neck carriage bolts?

      Short neck types suit thin boards and slim frames to avoid assembly protrusion and interference.

    • 5

      Q: What is Grade 5 carriage bolt strength level?

      Grade 5 heat-treated carriage bolts own higher tensile strength for heavy-duty structural fastening.

    • 6

      Q: Do stainless steel carriage bolts resist salt corrosion?

      316 stainless steel carriage bolts adapt perfectly to coastal salt fog and humid environments.

    • 7

      Q: Why do carriage bolts have round smooth heads?

      The domed smooth head prevents surface scratching and ensures safe, neat installation results.

    • 8

      Q: Can you customize non-standard carriage bolt sizes?

      A: We customize exclusive lengths, neck heights and coatings for special project installation demands.

    • 9

      Q: How to prevent carriage bolt rotation during tightening?

      A: The built-in square or ribbed neck embeds into materials to lock position and stop spinning automatically.

why sourcing your carriage bolts from sinsun is the right move

You have choices. Local hardware distributors with high markups and limited stock. Online marketplaces selling unbranded bolts with no traceability. Big industrial suppliers that treat carriage bolts as just another line item — no engineering guidance, no material verification, just a box shipped.

And we make cross‑border purchasing genuinely painless:

  • Pay in your local currency. Euro, Sterling, Australian Dollar, Brazilian Real, Turkish Lira, South African Rand, Indian Rupee, Thai Baht, and many more. No hidden wire fees. No exchange‑rate surprises.

  • Door‑to‑door logistics. Our in‑house logistics team handles customs clearance, port coordination, inland freight, and delivery to your warehouse. We ship to any major port worldwide.

  • Low MOQ for stock sizes. 100 pieces per size, and you can mix several diameters and grades in one container. Need a sample pack? We will send 5–10 pieces of each size you specify — no large commitment required.

  • Engineering support before you order. Not sure whether M10 HDG or A4‑80 stainless is right for your coastal deck project? Send us your site conditions, and we will recommend the exact grade, finish, and washer configuration. We do not guess — we consult the corrosion tables and building codes.

  • Full documentation with every order. Mill Test Certificate, hardness test results, dimensional verification, and — for stainless shipments — chemical composition analysis. We have provided audit‑ready documentation to government projects in Germany, Australia, and South Africa.

  • Ready to upgrade your timber connection specification?

request a bulk quote & free sample pack 

Get a full quotation within 8 working hours. Ask about our stock program for common M8 and M10 carriage bolts in Grade 8.8 HDG, A2 stainless, or A4 marine grade. We will send you certification samples, torque test reports, and a dimensional verification sheet before you commit to a production order. No pressure. No hidden small print. Just honest, certified carriage bolts from a team that actually reads the timber engineering standards.

Sinsun Carriage Bolts – Forged in China. Engineered for Timber.

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