Despite being a small component, fasteners are critical. There are so many types of fasteners available in the market, so we thought it would be great to write a buying guide. Even if you’re already familiar with fastener types and their uses, the below-given information would be helpful if you are planning to buy fasteners.
- Explaining fasteners
- Types of fasteners
- The common types of heads
- The most common types of drivers
- Types of fastener materials
- Grade/Class fastener strength
- Fastener coating material
- Types of threads and which one to choose
- Fasteners installed in corrosive environment
A fastener is a piece of hardware that is used to temporarily join two or more objects together. Generally, fasteners are non-permanent in nature, but they can be used to fasten or unfasten time and again without causing damage to the object.
Fastener nomenclature for metric series
Fastener nomenclature for inch series
1) The different types of fasteners
|Hex Bolt: These are generally used when it comes to construction and repair. They’re available in large variety of sizes and diameters.|
|Wood Screws: This has coarse threads, a thick shank, and an unthreaded portion of the shank. It is usually designed for wood or something similar.|
|Socket Cap Screws: They are generally used in machine parts and clamping.|
|Lag Bolts: They’re some of the toughest types of screws out there. They are generally used to connect heavy lumber and other materials that bear an intense load.|
|Carriage Bolts: It has a square shoulder with a rounded head. These bolts are used for wood-to-wood connections for blind holes.|
|Machine Screws: Machine screws have a consistent diameter the entire length of the shaft. They’re used to fasten machine components, appliances, etc.|
|Sheet Metal Screws: This is designed for connecting thinner metal objects or connecting metal to wood, plastic, and other materials.|
Fastener head style
|A countersunk head with a flat top.|
|A countersunk head with a rounded top.|
|A slightly rounded head with short vertical sides.|
|An extra wide head with a rounded top.|
|A hex head with a built-in washer.|
|A hex head with built-in washer and a slot.|
|A screw with a hexagonal head.|
|A small cylindrical head with a hexagonal drive hole.|
|A rounded head with a hexagonal drive hole.|
|A domed head with a slot.|
2) The most common drive types used with different fastener heads
|Spanner- It’s used to loosen and tighten nuts or bolts.|
|Phillips- The standard drive type for most screws. It has a four-star point at the end that fits into the corresponding screw’s shallow, cross-shaped depression.|
|Slotted- A slot head screwdriver has a single, flat blade that fits in the single slot of traditional screws.|
|Pozidriv- The screwdrivers have straight sided flanks, a blunt tip. Its tip resembles the Phillips cross-head configuration but with four additional wedges, making eight flanks altogether.|
|Socket, Hex, or Allen- A hex screwdriver features a hexagonal tip for driving certain nuts, bolts and screws. These screwdrivers can make the process of loosening and tightening hex nuts, bolts and screws much easier.|
|Star – A six-sided, star shaped screwdriver. It is designed to interact specifically with star screw heads.|
Types of fastener materials
- Steel Fasteners: Steel fasteners are commonly available in 4 grades.
- Stainless Steel & Aluminium: These materials are inherently resistant to corrosion. The strength of stainless is much less than alloy steel, and even less so for aluminum.
- Bronze and Brass: Bronze has high corrosion resistance quality. It is suitable for aquatic applications, such as underwater construction. Brass is somewhat similar to bronze in its anti-corrosive properties, but with slightly lower tensile strength because it is comparatively softer.
- Black Oxide: This provides very low protection against corrosion and usually coated with an oil film for extra protection.
- Hot-Dipped Galvanized: After stainless steel, this provides the best protection for outdoor use.
3) Grade/Class fastener strength
Fastener Grade/Class refers to the mechanical properties of the fastener material. Mostly, a bigger number indicates a stronger, more hardened (but also more brittle) fastener.
Grade 8 is the hardest, grade 5 is medium, and grade 2 is softer than 5 and 8. Grade 8 is commonly used in heavy manufacturing such as heavy tractors. Grade 5 is generally used in automobiles manufacturing. Grade 2 is used in household fasteners such as machine screws, nuts etc.
Grade 5 bolts have 3 lines on the head, grade 8 have a minimum of 6 lines on the head, and grade 2 have no lines at all. Mostly construction grade fasteners are grade 2. Metric nuts and bolts have quite similar grading system: Metric 8.8 is equivalent to a grade 5. Metric 10.9, 12.9, are equivalent to grade 8. Generally, mechanics choose grade 5 unless the manufacturer specifically needs grade 8 for safety issues.
4) Fasteners coating materials
Zinc, Zinc Dichromate, Cadmium, and Cadmium Dichromate coating is excellent for corrosion resistance. Galvanized and Black Zinc is also recommended to protect fasteners from corrosion. Chrome and Nickel have good resistance to corrosion in the normal atmosphere.
5) How are fasteners measured?
Fasteners are measured by diameter, length, and thread count. Diameter is how wide the shaft of the screw is. Diameter is usually measured outside the thread. Thread count is measured by TPI (thread per inch). The smaller the fastener the finer the thread. The length of a fastener is measured by its shank generally, the head is excluded. In the case of countersunk fasteners, the length is measured from the head including the shank.
Measuring a bolt
Measuring a countersunk screw
6) Types of threads and which one to choose
The most common thread types are the inch-based Unified coarse / fine (UNC/UNF) and metric coarse / fine. Coarse or Fine? To make it simple for you, use a coarse thread unless you’re tapping into sheet metal.
The differences are:
- Coarse threads have fewer threads per inch compared to fine threads.
- Coarse threads are more common than fine threads.
- Coarse threads allow for easier starting with less cross threading.
- Fine threads are approximately 10% stronger than coarse.
- Coarse threads can tolerate slight damage/corrosion than fine threads.
- Coarse threads are hard-wearing and have higher resistance to stripping.
Generally, a coarse thread is used for most of the industrial applications unless there is a strong reason not to do so. On metric fasteners, the coarse sizes are the most commonly used, for finer pitches are less readily available.
7) Installing fasteners in corrosive environments
The type of environment where the fasteners will be used plays a significant role in determining the coating needs. There are many types of fastener coatings especially used in corrosive environments including galvanizing, organic coating, electroless nickel plating, mechanical plating, zinc alloy plating etc. Some materials and environments including fire-retardants, ocean salt air and fertilizers can cause corrosion. When installed in corrosive environments fasteners can corrode and lose load-carrying capacity. It is evident that corrosion can cripple structures over time, but it is hard to anticipate the amount of weakening that can occur because corrosion rates can differ from location to location.
Buying fasteners is a time-consuming task; the purpose of this guide is to provide an overview of fasteners, including the materials, fastener types, application etc. This buying guide can help you find appropriate fasteners for almost any application. Whatever the fastening needs are, you can buy them on OfBusiness.com. Got questions? feel free to write to us.