Black Oxide & E-Coated
Lag Screws
Black oxide + sealant for harsh environments
Stripped-head resistant, wrench-ready drive
Perfect for cedar, redwood & visible applications
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Sinsun Black Lag Bolts: Heavy-Duty Fasteners with Premium Anti-Corrosion Coating
Shop Sinsun black lag bolts (black lag screws / black coach bolts) with premium corrosion-resistant coating. Ideal for exterior decking, timber framing & marine applications. 1/4" to 3/4" diameters. Factory direct pricing. Get a quote today!
Get a Quick QouteSinsun Black Lag Bolts - Industrial Grade Rust-Resistant Black Coated Lag Screws
Whenever structural integrity and aesthetic precision are needed, Sinsun Black Lag Bolts are the best choice. Also called black lag screws or dark coach bolts, these heavy-duty fasteners have a high-quality rust-resistant coating that comes in a black oxide or electro-deposition (e-coat) finish. This coating makes them more resistant to rust and stops the ugly rust bleeding that happens with regularly zinc-plated fasteners. Our black lag bolts are made for industrial-grade holding power.Their deep coarse threads and high-strength carbon steel core make it difficult to remove them from load-bearing timber connections.
Sinsun brings decades of fastening expertise to every black lag bolt we manufacture. Cold-heading technology, multi-stage coating processes, and rigorous quality control protocols are used in our production facilities to ensure dimensional accuracy and coating uniformity. We guarantee consistent quality, competitive pricing, and reliable stock availability, whether you're ordering bulk quantities for a commercial project or custom sizes for a specialized project.
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Premium Black Coating Technology: Our black coating comes in black oxide (military-spec) or E-coat finish. It forms a strong barrier against moisture and oxygen, stopping red rust from forming and giving the surface a smooth, even look.
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Deep, Aggressive Coarse Threads: The sharp, deep-thread design ensures that the screws grip well in both softwoods and hardwoods. This makes them more difficult to pull out of and less likely to come loose when under dynamic loads.
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Hex Head Ready for Wrenching: The hex head is made to fit perfectly with standard wrenches or sockets, so you won't have to worry about cam-out and you'll always get a tight fit.
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Works with ACQ: Our black lag bolts are compatible with alkaline copper quat (ACQ) treated lumber. They don't react to chemicals that accelerate corrosion in pressure-treated wood applications.
| Parameter | Specification |
| Material | High-Carbon Steel / Alloy Steel |
| Standard | ASTM A307, ASME B18.2.1 (Inch), DIN 571 (Metric) |
| Coating Type | Black Oxide (Military Spec) / E-Coat (Electro-deposition) / Black Phosphate |
| Coating Thickness | 5–15 µm (Black Oxide) / 15–25 µm (E-coat) |
| Head Type | Heavy Duty Hex Head |
| Drive Type | External Hex (Socket/Wrench Drive) |
| Thread Type | Coarse, Sharp Lag Thread (ASME / DIN Standard) |
| Point Type | Gimlet Point / Cone Point |
| Length Range | 1" to 12" (25mm to 300mm) |
| Diameter Range | 1/4" to 3/4" (M6 to M20) |
| Corrosion Resistance | 72–96 hrs Salt Spray (Black Oxide) / 200+ hrs (E-coat) |
| Temperature Range | -40°F to 300°F (-40°C to 150°C) |
| Application | Wood-to-Wood, Wood-to-Metal, with Shields in Masonry |
| Certification | ISO 9001:2015, RoHS Compliant |
| Size (Diameter x Length) | Threads Per Inch (TPI) | Head Size (Width) | Wrench Size | Shank Diameter | Coating Type | Standard |
| 1/4" x 1-1/2" | 10 TPI | 7/16" | 7/16" | 0.25" | Black Oxide / E-coat | ASME B18.2.1 |
| 1/4" x 3" | 10 TPI | 7/16" | 7/16" | 0.25" | Black Oxide / E-coat | ASME B18.2.1 |
| 5/16" x 2" | 9 TPI | 1/2" | 1/2" | 0.3125" | Black Oxide / E-coat | ASME B18.2.1 |
| 5/16" x 3" | 9 TPI | 1/2" | 1/2" | 0.3125" | Black Oxide / E-coat | ASME B18.2.1 |
| 3/8" x 3" | 7 TPI | 9/16" | 9/16" | 0.375" | Black Oxide / E-coat | ASME B18.2.1 |
| 3/8" x 4" | 7 TPI | 9/16" | 9/16" | 0.375" | Black Oxide / E-coat | ASME B18.2.1 |
| 3/8" x 6" | 7 TPI | 9/16" | 9/16" | 0.375" | Black Oxide / E-coat | ASME B18.2.1 |
| 1/2" x 4" | 6 TPI | 3/4" | 3/4" | 0.5" | Black Oxide / E-coat | ASME B18.2.1 |
| 1/2" x 5" | 6 TPI | 3/4" | 3/4" | 0.5" | Black Oxide / E-coat | ASME B18.2.1 |
| 1/2" x 6" | 6 TPI | 3/4" | 3/4" | 0.5" | Black Oxide / E-coat | ASME B18.2.1 |
| M8 x 80mm | (1.25mm Pitch) | 13mm | 13mm | 8mm | Black Oxide | DIN 571 |
| M10 x 100mm | (1.5mm Pitch) | 17mm | 17mm | 10mm | Black Oxide | DIN 571 |
| M12 x 150mm | (1.75mm Pitch) | 19mm | 19mm | 12mm | Black Oxide | DIN 571 |
Black Lag Bolts: Main Uses
People choose black lag bolts for both their looks and their ability to do their job. They usually have a black oxide finish. The black finish protects against mild corrosion and gets rid of the shiny glare that comes with regular zinc-plated hardware.
Putting together outdoor furniture
Black lag bolts are the most effective way to build high-end outdoor furniture like picnic tables, Adirondack chairs, and benches. The dark finish works well with dark-stained hardwoods like cedar, redwood, and pressure-treated pine. This means you don't have to hide or paint the fasteners. Black lag bolts blend in with the wood grain, giving a clean, professional look. Shiny galvanized bolts, on the other hand, reflect sunlight and draw attention. The rough threads hold very well in softwood, keeping joints tight even after years of outdoor use and temperature changes. The black oxide coating protects furniture from rain and humidity while keeping its original looks.
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Playground equipment installation
Black turnbuckles are widely used during playground equipment installation in municipal and residential areas due to their combination of safety and aesthetic appeal. In addition to preventing distractions for children, their non-reflective surfaces maintain clear visibility for supervisors. Black turnbuckles securely attach swing sets, climbing structures and rock wall supports to wooden frameworks. Furthermore, their dark colour enables the fasteners to blend seamlessly into the background, preventing visual clutter.
These bolts must also comply with ASTM playground equipment safety standards and withstand shear loads generated by children's dynamic activities. NewShun black lag bolts feature deep threading to prevent loosening caused by continuous vibration and movement, ensuring structural integrity in high-traffic environments.
Wood Frame Construction
It is common to use black pull bolts in exposed wood frame construction to serve both as structural fasteners and as design elements. When hardware remains visible in finished buildings—such as barn-style residences, restaurant interiors, and commercial spaces with rustic design themes—architects and builders specify black oxide fasteners.
This finish complements wrought iron hardware, dark steel accents, and industrial design elements. These structural connections require bolts that provide shear strength as well as pull-out resistance while maintaining visual appeal. The “Sinsun” brand 1/2-inch and 5/8-inch diameter black pull bolts deliver the load-bearing capacity required for beam connections, column anchoring, and knee brace fastening in heavy timber structures.
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Hardware for gates and fences
Black lag bolts that match powder-coated hardware and dark-stained fencing materials are suitable for gates and fences. Its non-reflective finish blends in with cedar, pine, and composite fencing materials, giving it an aesthetically pleasing look that homeowners prefer over shiny galvanized hardware.Fence panels, latch mechanisms, and gate hinges are connected to fence posts with black lag bolts. The coarse threads grip treated wood very well. The low-visibility fasteners make it less likely that people will mess with the fence by not drawing attention to the connection points. The black oxide coating protects the fence well and keeps the gate hardware looking the same as black-painted or powder-coated hardware.
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Industrial equipment mounting
Manufacturing facilities and warehouses use black lag bolts to secure equipment, machinery, and storage systems to wooden blocks and structures. The dark finish offers mild corrosion resistance in interior and industrial environments while providing a professional appearance that doesn't show shop dust and grime as readily as bright plated fasteners. The shear strength of black lag bolts ensures the stability of equipment mounts, conveyor supports, and heavy shelving systems under continuous vibration and load. Sinsun black lag bolts are available in lengths up to 8 inches, allowing deep penetration into structural wood members for maximum holding capacity.
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Building Sets for Events and Theater
The dark finish of black lag bolts blends in with painted backdrops and does not reflect stage lighting, which make them ideal for stage sets, exhibition booths, and temporary event structures.Set designers like that black oxide fasteners don't need to be painted over after installation and won't reflect light during performances. These uses need bolts that can be put in and taken out many times without damaging the threads. The black oxide finish is perfect for rental inventory and set pieces that can be used again and again. The bolts need to hold things together well without being too obvious, so the audience can focus on the performance instead of the hardware that holds the set together.
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1.Professional fastener manufacturers:
As a specialized fastener manufacturer focused on industrial-grade stud production, Sinsun brings decades of experience to the table. Unlike traders or assemblers, we control every production stage—from raw material procurement to final coating application.
2.Precision coating technology:
We use advanced processes to ensure uniform coating thickness, complete coverage, and exceptional adhesion on our black coating production line.Whether it's military-grade black oxidation treatment or heavy-duty electrophoretic coating, Sinsun guarantees consistent quality across all batches.
3.Comprehensive Quality Control:
in addition to dimensional verification with optical comparators, each batch undergoes a rigorous inspection process. It also includes coating thickness measurement, salt spray testing for corrosion resistance, and torque testing to validate thread strength.
4.All Sizes Available
We have a lot of stock in all the most common sizes and lengths, from 1/4" to 3/4" and 1" to 12". There are no minimum order amounts for stock sizes, and you can get volume discounts on full container loads.
5.Custom Manufacturing Capabilities
Do you need a length that isn't standard? Markings on the head? Packaging made just for you? Sinsun can make things to your exact specifications using OEM services. Send us your drawings, and we'll figure out how to make it work.
6.Competitive Factory-Direct Pricing
We cut out the middleman by making things ourselves and selling them directly. You get industrial quality at wholesale prices, no matter if you're a distributor, contractor, or OEM buyer.
7.Global Export Experience
Trusted by customers across Europe, Australia, Southeast Asia, and the Middle East, Sinsun understands international shipping, documentation, and quality standards required for global projects.
8.Long-Term Reliability
Our black lag bolts are engineered for decades of service. The combination of high-strength steel and advanced coating technology ensures your structures remain secure and rust-free for years to come.
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Q: How do black oxide lag bolts differ from e-coat black lag bolts?
A: Black oxide is a conversion coating that protects against rust for a short time (72–96 hours of salt spray) and gives things a sleek, dark look. It's great for indoor or sheltered outdoor use where looks are important. E-coat (electro-deposition coating) is a paint-like coating that is applied with electricity. It is better for direct outdoor exposure and marine environments because it is thicker and better at resisting corrosion (200+ hours of salt spray).
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Q: Will Sinsun black lag bolts rust if used outside?
A: Our black lag bolts are made to not rust when used outside. Our advanced black coating and high-strength steel work together to keep moisture and humidity out very well. If you live in a place with a lot of saltwater or marine life, we suggest our e-coat finish or upgrading to 316 stainless steel.
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Q: Do black lag bolts leave marks on redwood or cedar?
A: No. One of the best things about Sinsun black lag bolts is that they won't bleed or stain high-quality woods like cedar, redwood, or pressure-treated lumber. Zinc and galvanized fasteners can leave dark streaks as they weather, but our black coating stays stable and doesn't leach.
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Q: How big of a pilot hole should I drill for black lag bolts?
A: To get the best grip and keep the wood from splitting, drill a pilot hole that is about 75% of the bolt's shank diameter. As an example, drill a 3/8" pilot hole for a lag bolt that is 1/2" wide. The pilot hole can be a little smaller in softwoods and a little bigger in hardwoods, closer to the shank diameter.
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Q: Is it possible to use Sinsun black lag bolts in concrete or brick?
A: Yes, but they need a lag shield (expansion shield) or a masonry anchor. After the shield is set in the concrete, the lag bolt goes through the threads. Instead of shields, you can use our concrete screw anchors to fasten masonry directly.
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Q: Do you have special coatings or lengths that are made to order?
A: Yes, of course. Sinsun is an expert in making things to order. We can make black lag bolts in lengths that aren't standard, with special markings on the heads, or with custom coating specifications to fit your project's needs. Get in touch with our sales team to let them know what you need.
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Q: Will the powder coating crack or peel during installation?
A: Sinsun powder coated lag screws undergo a curing process that creates a flexible bond. When installed with proper pilot holes, the coating withstands normal driving torque without cracking or peeling .
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Q: What tools do I need to install square head lag bolts?
A: Use an adjustable wrench, open-end wrench, or a socket with a square drive adapter. For restoration work, a traditional carpenter's wrench is also suitable .
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Q: Are these screws available in metric sizes?
A: Yes. Sinsun offers black square head lag screws in both imperial diameters (1/4" to 3/4") and metric diameters (M6 to M20) to suit global project requirements .
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Q: Are decorative lag bolts as strong as structural grades?
A: Yes. Decorative does not mean reduced strength. These bolts meet the same ASTM A307 strength standards as industrial grades—they simply offer a better finish for visible applications .
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