Choosing the right fasteners is not easy, but it is very important for the structural integrity of large construction projects like building a terrace or strengthening a heavy timber frame. A lot of people talk about carriage screws and bolts. Are they the same? If not, which one should you choose?
In short: they actually refer to the same type of fastener. In North America, the word “bolt” is used most of the time. In Britain and Australia, the word “carriage screw” is used most of the time. Sinsun makes these strong, flexible fasteners to the highest standards, so your projects will last a long time.
Let’s talk about what they are and how to use them.
The Parts of a Heavy-Duty Fastener
It doesn’t matter if you call it a Lag Bolt or a Coach Screw; it has a unique design that makes it different from regular screws or bolts:
Hex Head: Has a hexagonal head that needs a wrench or socket to install. This lets you get a lot of torque and a very tight clamp.
Partially Threaded Shank: The shank is smooth near the head and has threads that go toward the point. This design lets the unthreaded part work as a shear plane, which makes it stronger for heavy loads.
Sharp Point: Made to make it easier to get into wood.
A Comparison of Sinsun Lag Bolts and Coach Screws
The table below lists the most important features of this type of fastener, which can help you choose the right Sinsun product for your job.
Feature | Description & Sinsun Specifications |
Common Names | Lag Bolt (North America), Coach Screw (UK/Australia) |
Head Type | Hexagonal Head (Hex Bolt). Sinsun provides a true hex head for a secure wrench grip, preventing stripping. |
Drive Method | Wrench (or impact driver with a hex adapter). Cannot be driven with a standard screwdriver bit. |
Threading | Coarse, sharp threads designed for a powerful grip in wood, particle board, and other soft materials. |
Typical Diameters | 1/4″ (6mm) to 1″ (25mm) and larger. Common sizes for decking are 3/8″ and 1/2″. |
Typical Lengths | 1 inch (25mm) to 12+ inches (300mm). Sinsun offers a full range to meet any project depth. |
Primary Material | Low-Carbon Steel, High-Strength Steel, Hot-Dipped Galvanized (HDG), Stainless Steel (304/316). |
Key Applications | – Heavy Timber Construction (e.g., post-and-beam structures) – Ledger Boards (critical for deck safety) – Utility Poles & Fencing – Fastening metal brackets, hangers, and hinges to wood. |
A closer look at the Sinsun advantage in designing threads and heads
Not every lag bolt is the same. Sinsun designs its fasteners to work best:
Thread Design: Our coarse threads are cut and hardened just right so they don’t strip the wood. The sharp leading edge helps make installation easier by decreasing the driving torque required without affecting holding power
Head and Washer Integration: A lot of our lag bolts have a square washer (flange) built into the hex head. This spreads the clamping force over a larger area, which stops the head from sinking into the wood and hurting it, which is very important for softwoods.
hoosing the Right Sinsun Fastener for the Job
You don’t usually have to choose between a lag bolt and a coach screw. Instead, you need to choose the right size, material, and coating for the job.
For ledger boards and decks outside: This is a very important use where failure is not an option. The ledger board is what holds your deck up.
We suggest using Sinsun Hot-Dipped Galvanized (HDG) or 304 Stainless Steel lag bolts.
Why: HDG has a thick zinc coating that protects against rust for decades. To stop salt from corroding, 304 or 316 stainless steel is required in coastal areas.
A 1/2″ diameter by 4-5″ long bolt is common, but you should always follow local building codes.
Don’t give up on your foundation, conclusion
There is no doubt of what a Lag Bolt or a Coach Screw does: they provide a very strong, reliable connection in tough situations. When you choose Sinsun, you’re not just buying a fastener; you’re also making your project safer and longer-lasting.
Are you ready to build with confidence? On our product page, you can see all of the Sinsun Lag Bolts and Coach Screws, along with detailed information about their specs and how to protect them from rust.
