Bolts are used to connect and constrain materials. To do that, they must be a good fit physically and functionally.
Luckily, key measurements and standards can help you narrow down bolt options. Inch and metric fastener size names communicate the same basic actual measurements: Outside Diameter (OD) and Threads Per Inch (TPI). You can also look for strength grade markings, which use line indentations or numbers.
Materials
The materials used to make bolts determine their strength, lifespan, and cost. They also affect how they handle rust and weather. Bolts are typically made from durable and rust-resistant metals like iron, steel, or aluminum alloys. They can be coated with different finishes to prevent corrosion and handle specific environmental conditions.
For example, a zinc bolt does well in indoor and dry conditions. The hot-dipped galvanized finish protects against rust and makes it suitable for outdoor use. Stainless steel bolts have varying amounts of chromium that change the way they respond to heat, acids, and corrosion.
Although there are differences between inch and metric fasteners, their basic measurements remain the same. Bolt sizes are named based on key measurements, standards, and strength grade markings. For example, a 1/2’’-20 bolt has a designated diameter and threads per inch (TPI). The head type, finish, and thread pitch are also important factors when selecting a bolt. These numbers are printed on the bolt’s head and indicate how much stress it can withstand.
Threads
The varying standards of threaded fasteners can be confusing to track. Fortunately, Bayou City Bolt’s engineers and representatives can help your organization keep up with the endless variations of threaded hardware that has driven human progress for millennia.
In general, the size of a bolt is given by its diameter and threads per inch (TPI). The first number is the bolt’s outside diameter and the second indicates how many threads are on one inch of the bolt’s length.
TPI is important because it determines a fastener’s strength and tensile stress area. For example, a screw with a greater thread pitch has more tensile stress than a screw with a lower thread pitch.
In addition, threads can be categorized into coarse, fine, and super-fine. Coarse threads are good for general use, while fine threads offer more holding force and are better suited for precision applications. Finally, threads can also be left hand or right hand. Right hand threads are turned clockwise, while left hand threads are turned counterclockwise.
Length
When determining the size of your bolt, there are two important dimensions to consider: diameter and length. The diameter is the distance across the bolt’s shank or threaded area, and it is usually measured using a caliper or a bolt gauge.
The length is the distance from the underside of the bolt head to the end of the shaft. Hex bolts are normally measured from the underside of the head, while pan and button head bolts are measured from the center of the shaft.
Some bolts are regulated by strength standards set by the ASTM and the military, such as AN (Air Force-Navy) and MS or NAS (Military Specification). These bolts typically have different markings and may be slightly shorter than standard inch bolts. However, they have high tensile and yield strengths. They also resist chemical solvent attacks and are electrically insulating. These characteristics make them an ideal choice for aircraft and military applications. In addition, they are non-corrosive and self-extinguish if exposed to fire.
Finish
The finish of a bolt is the plating or coating applied to it. This is done to improve the strength of the bolt and its resistance to corrosion or wear. It is also used to enhance its appearance. Common finishes include rust resistant metal, hot dip galvanized, and black oxide. Phosphating is often used for high-strength bolts to avoid hydrogen embrittlement. This is accomplished by putting the bolts into tanks of varying concentrations of an alkaline solution such as lye and then water. Stainless steel bolts are often plated in either electro-zinc or cadmium because they don’t react with the wood, unlike other metals like brass and silicon bronze.
Inch bolts have a number of important dimensions including the diameter, length, thread pitch and head size. They are also graded (imperial) or classed (metric) to indicate their tensile strength, which is the amount of stress or stretch that they can handle before breaking. This information can be found on the head of the bolt or in a chart.
