Inch bolts are used to hold things together. They are found everywhere from home improvement projects to aerospace technology, and each bolt type serves a different purpose. Bolts can be made of a variety of materials and undergo many different heat treatments to increase or decrease their strength, corrosion resistance, hardness and other properties. Bolts are also categorized by grade (imperial system) or class (metric system), which determines the maximum stress and stretch they can handle before breaking. In both systems, bolt grades are indicated by a series of raised dashes on the head of the fastener.
When selecting a bolt, the most important thing to consider is its function. The size, grade and other characteristics of the bolt should reflect the requirements of the application. Bolts are available in a wide range of sizes and types, so it is important to know how to distinguish between them. There are several ways to identify the size of a bolt, including looking at the head of the screw or bolt, measuring the diameter of the threads using a ruler or tape measure, or reading the information on the bolt’s packaging or in the bolt’s identification markings.
The most common type of bolt is the hex bolt, which has six sides and can be turned by hand. It is the most commonly used fastener in the world and can be seen on furniture, vehicles and many other products. The hex bolt has an internal thread that is covered with a flange that acts as a washer and helps distribute the load.
Other bolts have a pointed end, such as the eye bolt, which has a loop at the base of its head. This fastener is often used to suspend electrical conduits, fixtures or sheet metal from a wall or ceiling. The eye bolt can be installed with a nut at the bottom of its loop to secure it in place. Eye bolts are available in a wide range of lengths, diameters and thread pitches.
In order to select the correct bolt for your project, you need to understand how to read the identification markings on the bolt head. The first number on the bolt callout indicates its diameter in inches, followed by a fraction that represents the number of threads per inch (TPI). The final number is the fastener’s length. Bolts with diameters less than 1 inch may be listed with two possible TPI configurations (coarse or fine). Bolts with diameters greater than 1 inch have a single TPI configuration.
Metric bolts have a similar designation scheme, with the first number representing the nominal diameter in millimeters and the second number indicating the thread pitch. The threads on metric bolts are coarser than those of standard Inch screws, and they require more rotations to install them. The difference in TPI between the two fasteners will not make a significant difference in their tensile strength, but the coarser threads do provide better clearance for thread plating and are less likely to gall or strip.