How does the cup square (carriage bolt) neck prevent the bolt from spinning?

The square section directly beneath the dome head bites into the material — typically wood — as the nut is tightened, locking the bolt in place without needing a wrench on the bolt head. This makes installation faster and leaves a clean, tool-free finish on the visible face.

M6 Carriage Bolts A2 Stainless Steel — Cup Square Coach Bolt with Dome Head, M6×12mm to M6×60mm - HomeDIYer

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M6 Carriage Bolts A2 Stainless Steel — Cup Square Coach Bolt with Dome Head, M6×12mm to M6×60mm

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size option: M6*12

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M6 Carriage Bolts in A2 Stainless Steel — Secure, Rust-Resistant Fastening for Wood & Outdoor Projects

Stripped threads, spinning bolt heads, and rust stains on your finished woodwork — these are the frustrations that send DIYers and contractors back to the hardware store mid-project. Whether you're building a backyard deck, assembling a timber frame, or hanging a gate, you need a fastener that stays put, looks clean, and holds up to the elements. These M6 cup square carriage bolts are designed for exactly that.

Each bolt is machined from A2 (304) stainless steel and features a smooth dome head with a square-shouldered neck that self-locks into wood without a second wrench. Available in 11 lengths from 12mm (½") to 60mm (2⅜") and in packs of 5, 10, or 20, they cover everything from thin panel joints to thick structural timbers. The M6 metric thread (1.0mm pitch) pairs with any standard M6 nut and washer.

Typical applications include deck board fastening, pergola and fence construction, timber furniture assembly, and general outdoor woodworking — anywhere you need a flush, tamper-resistant bolt face with reliable clamping force on the nut side.

🔩 Compatibility: M6 metric thread (pitch 1.0mm) — fits all standard M6 nuts and washers. Not compatible with imperial (SAE/UNC/UNF) fasteners. Square neck is designed for use in wood; pre-drilling is recommended for hardwoods.

✅ Key Features of These M6 Stainless Steel Carriage Bolts

🛡️ A2 Stainless Steel Construction — Grade 304 stainless resists rust, oxidation, and staining in outdoor, humid, and light marine environments without surface coatings that can chip or peel.
🔒 Self-Locking Cup Square Neck — The square shoulder beneath the dome head embeds into wood as the nut is tightened, preventing rotation and eliminating the need for a second tool on the bolt side.
✨ Clean Dome Head Finish — The low-profile rounded head sits flush and smooth on the visible face of your workpiece — ideal for deck boards, furniture, and any application where appearance matters.
📏 11 Lengths from 12mm to 60mm — From 12mm (½") for thin panel joints to 60mm (2⅜") for thick structural timbers, one listing covers the full range of common M6 carriage bolt applications.
📦 Flexible Pack Sizes (5 / 10 / 20 pcs) — Order exactly what your project needs. The 20-piece pack offers the lowest per-unit cost for larger builds or when keeping spares on hand.
⚙️ Standard M6 Metric Thread (1.0mm Pitch) — Fully compatible with any M6 metric nut, wing nut, or washer. No proprietary hardware required — easy to source replacements anywhere.

📐 Technical Specifications — M6 Cup Square Carriage Bolts

Thread Size	M6 (6mm diameter, 1.0mm pitch)
Available Lengths	12mm (½"), 16mm (⅝"), 20mm (¾"), 25mm (1"), 30mm (1³⁄₁₆"), 35mm (1⅜"), 40mm (1⁹⁄₁₆"), 45mm (1¾"), 50mm (2"), 55mm (2³⁄₁₆"), 60mm (2⅜")
Pack Sizes	5 pieces, 10 pieces, 20 pieces
Head Type	Dome (round) head — cup square carriage bolt profile
Neck Type	Cup square (self-locking in wood)
Material	A2 Stainless Steel (Grade 304)
Finish	Natural stainless (no coating)
Tensile Strength	Typically 500–700 MPa (A2-50 to A2-70 class)
Thread Standard	ISO metric coarse thread
Drive Type	No drive (nut-side tightening only)
Compatible Nut	Standard M6 metric hex nut (sold separately)
Recommended Use	Wood, timber, decking, fencing, furniture assembly
Corrosion Resistance	Good — suitable for outdoor and humid environments; see note for marine use
Country of Origin	See variant options

⚠️ Marine or highly corrosive environments: A2 stainless steel performs well in most outdoor conditions, but for saltwater or coastal exposure, A4 (316) stainless steel is generally recommended. Contact us to confirm suitability for your specific application.

❓ Frequently Asked Questions

How do I choose the right length for M6 carriage bolts?

Add up the total thickness of all materials being joined, then add approximately 10–15mm to allow for a washer and nut. For example, joining two 20mm (¾") boards typically calls for an M6×50mm bolt. Lengths available here range from 12mm (½") to 60mm (2⅜"), covering most standard timber and panel thicknesses.

What does A2 stainless steel mean, and how strong are these bolts?

A2 stainless steel — also known as Grade 304 — is the most widely used austenitic stainless alloy. It offers good corrosion resistance and a tensile strength of generally 500–700 MPa depending on the property class (A2-50 or A2-70). This makes it suitable for most structural woodworking, furniture, and outdoor fastening applications.

Can these M6 carriage bolts be used outdoors or in wet environments?

Yes. A2 stainless steel resists rust and oxidation in most outdoor, humid, and freshwater environments without any additional coating. For highly corrosive settings — such as coastal, marine, or chemical-exposure environments — A4 (316) stainless steel is generally the better choice. Contact us if you need guidance for your specific conditions.

What nut and washer thread standard do these bolts use?

These bolts use a standard ISO metric M6 coarse thread with a 1.0mm pitch. They are compatible with any M6 metric hex nut, wing nut, or washer. They are not compatible with imperial (SAE, UNC, or UNF) fasteners — do not mix metric and imperial hardware.

How does the cup square neck stop the bolt from spinning during installation?

The square section directly beneath the dome head is slightly larger than the shank. As you tighten the nut, this square shoulder bites into the surrounding wood, locking the bolt in place. This means you only need a wrench on the nut side — no need to hold the bolt head, and no tool marks on the finished face of your workpiece.

Do I need a washer with these carriage bolts?

A flat washer under the nut is generally recommended. It distributes the clamping load over a wider area, reducing the chance of the nut pulling through softer wood. The dome head side typically does not require a washer — it sits flush against the material surface by design.

Which pack size should I order — 5, 10, or 20 pieces?

The 5-piece pack suits small repairs or single-joint projects. The 10-piece pack covers most deck board runs, fence panels, or furniture builds. The 20-piece pack offers the best per-unit value for larger projects or when you want extras on hand for future repairs. All pack sizes are available across all 11 lengths.

🛒 Select your size and quantity above, then add to cart — ships from our US warehouse.

M6 Carriage Bolts A2 Stainless Steel — Cup Square Coach Bolt with Dome Head, M6×12mm to M6×60mm

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M6 Carriage Bolts in A2 Stainless Steel — Secure, Rust-Resistant Fastening for Wood & Outdoor Projects

✅ Key Features of These M6 Stainless Steel Carriage Bolts

📐 Technical Specifications — M6 Cup Square Carriage Bolts

❓ Frequently Asked Questions

M6 Carriage Bolts A2 Stainless Steel — Cup Square Coach Bolt with Dome Head, M6×12mm to M6×60mm

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