Bolts are indispensable components found in machines that we encounter daily. In fact, bolts are one of the most common and diverse fasteners on the market. Bolts come in a variety of shapes and sizes which will determine their application. In this blog, we will discuss how a bolt works, what the different types are, and the difference between a bolt and a screw.
Simply, bolts are a type of threaded fastener used to clamp two separate parts together. They are commonly made of steel, brass, bronze, titanium, or any other metal that provides corrosion resistance and is not easily deformed. The anatomy of a bolt is relatively straightforward and varies little between types. The head is the visible part of the bolt, which is the widest in diameter and prevents axial movement. A shank is the unthreaded part of the bolt and works to prevent radial movement of the parts being secured. The unthreaded shank provides less abrasion and more precise contact with the parts surrounding the bolt. The thread is the portion of the bolt a nut screws over to provide clamping force.
When it comes down to picking the optimal fastener, there are eight types of bolts that vary in shape and application which can be chosen from: 1. Anchor Bolt: These bolts feature a narrow "I" shaped head and typically use a nut and washer to be tightened down. Their primary use is to connect objects to concrete and provide resistance against shear forces. 2. Carriage Bolt: Carriage bolts contain a unique, shallow mushroom-shaped head that is resistant to turning once the bolt is tightened. They are most compatible with wood-to-wood connections and are commonly used for projects that require a smooth finish. 3. Eye Bolt: Eye bolts are an easily recognizable bolt that feature a loop or ring at one end. This loop allows ropes and strings to be threaded through, assisting with vertical lifting. 4. Hanger Bolt: These bolts contain no heads and are threaded at both ends. They only fit into pre-drilled holes and are typically used to help permanently affix wooden and metal objects. 5. Hex Bolt: As the name suggests, hex bolts are made with a six-sided head. These bolts are the most prevalent in industrial settings and are used in various applications, including aircraft, highway structures, and buildings. 6. Square Head Bolt: Prior to the popularization of hex bolts, square head bolts were the industry standard. Their square head designs allow for an easier wrench grip for tightening. Today, these are much harder to find and generally need to be custom-made to replace fasteners in an older machine or structure. 7. U-Bolt: Used to secure pipes or tubing, U-bolts are curved bolts that are threaded on either end. 8. Lag Bolt: These bolts are usually the largest and toughest of the fasteners listed. They are often used for lumber, concrete, or any other material that is constantly exposed to a heavy load.
While similar in their applications and function, the commonly held belief that screws and bolts are the same is incorrect. The primary difference is that bolts fasten two unthreaded objects, while screws will either need to create a thread in the object or have one in place. Also, screws are always threaded up to the head, whereas a bolt typically has an unthreaded shank.
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