A bolt is a long metal piece with a threaded end that holds fasteners in place. Its body is usually round and it has a helix-like thread that runs around the entire length. Bolts come in different sizes, which are designated by a combination of numbers and letters. The number is the major diameter and the letter indicates the thread pitch, or how many threads are per inch. A larger number means a finer thread and a smaller one is coarse. The standard system of sizing is called SAE, while the metric system is used in Europe and Japan.
SAE stands for the Society of Automotive Engineers, and its standards are among the most common for inch hardware. They cover a wide range of bolts, screws, and other types of hardware. In addition to identifying how many threads are per inch, these specifications include the tensile strength of the bolt. The higher the grade of a bolt, the stronger it is.
Typically, SAE bolts are made of carbon steel, though some can be made from high-strength alloy metals. Each type of bolt has a different tensile strength requirement and has special markings on its head that indicate the grade. Bolts with the highest tensile strength are used in critical applications. Bolts with the lowest tensile strength are used in non-critical applications and are not as strong as their higher-grade counterparts.
There are also varying degrees of quality when it comes to SAE bolts. Some are considered “commercial” grade, which is generally suitable for most applications. Others are considered “industrial” or “high-strength,” which is intended for heavy duty use. Industrial-grade bolts can be used in construction projects, machinery or vehicles and are designed to meet a higher level of stress and load requirements than commercial-grade bolts.
Unlike most other forms of hardware, bolts are often labeled by their major diameter rather than their thread pitch. They are usually designated as either UNC or UNF, which are abbreviations of the terms Unified National Coarse and Unified National Fine. The more threads are in an inch, the finer the threads. Using a finer thread is generally preferred, as it provides greater holding power and is easier to remove if the fastener needs to be replaced.
Most bolts are marked with their strength grade on their heads, but the grades can be hard to read if they are not clearly stamped. The most important factor when determining a bolt’s strength is the amount of force required to break it. This information can be found in the product specifications or in a technical document available from the manufacturer. The tensile strength is generally stated as a minimum value and may be exceeded by certain factors, including: temperature, corrosion, coatings, surface finish, and the amount of torque applied during tightening. The tensile strength may also vary due to the length of time a bolt is under load, which can lead to fatigue. All bolts, regardless of their grade, must be inspected after each use to ensure they are not damaged or subjected to excessive stress or strain. SAE bolts