Carriage bolt, also known as a coach bolt, is a type of fastener designed to be used with wood, typically in construction and woodworking applications.
The bolt has a smooth, dome-shaped head and a square section immediately beneath it, which grips into the wood to prevent the bolt from turning when tightened. The remainder of the bolt is threaded, allowing a nut to be screwed onto it to secure the bolt in place.
Carriage bolts are commonly used in a variety of applications where a strong, secure joint is required, such as in the construction of decks, docks, and fences. They are also used in the assembly of furniture, playground equipment, and other wooden structures where a neat appearance is desired, as the smooth head of the bolt sits flush with the surface of the wood.
head of a carriage bolt is typically round and domed, which provides a finished appearance and distributes the load evenly. Some carriage bolts have a square neck beneath the head to keep the bolt from turning.
Shank: The shank is the straight portion of the bolt that extends from the head to the end. It is typically smooth and without threads, except for a short section near the end of the bolt.
Thread: Carriage bolts have partial threads that extend from the end of the shank to about halfway up the bolt. This allows the bolt to be screwed into a pre-threaded hole, while the unthreaded section of the shank provides greater shear strength.
Square Shoulder: A square shoulder, also known as a square neck, is a feature found on some carriage bolts that helps keep the bolt from turning when installed. The square shoulder fits into a square hole on the material being fastened, preventing the bolt from turning while the nut is being tightened.
Material: Carriage bolts can be made from a variety of materials, including stainless steel, brass, and zinc-plated steel. The material used depends on the application and the environmental conditions that the bolt will be exposed to.
Size: Carriage bolts are available in various sizes, including diameter and length, to accommodate different applications. The diameter of the bolt determines the strength of the bolt, while the length of the bolt depends on the thickness of the materials being fastened together.
Diameter (mm) | Thread Pitch (mm) | Head Diameter (mm) | Head Height (mm) | Square Neck Width (mm) | Square Neck Depth (mm) |
---|---|---|---|---|---|
6 | 1 | 12 | 5.7 | 10 | 3.8 |
8 | 1.25 | 16 | 7.5 | 13 | 5.3 |
10 | 1.5 | 20 | 9.2 | 16 | 6.8 |
12 | 1.75 | 24 | 11.1 | 18 | 7.5 |
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