Mutual Screw's Ultimate Guide to Fasteners: Types, Uses, and How to Choose
Fasteners are the unsung heroes of the engineering, construction, and manufacturing world. They are the hardware devices that mechanically join or affix two or more objects together. From the towering skyscrapers defining our city skylines to the smartphone in your pocket, fasteners are everywhere, holding our world together.
This comprehensive guide will walk you through the most common types of fasteners, their specific characteristics, and their typical applications. Whether you're a seasoned professional or a DIY enthusiast, understanding the different types of fasteners is crucial for the success and safety of any project.
1. Bolts
A bolt is a form of threaded fastener with an external male thread. Bolts are typically used in conjunction with a nut to connect unthreaded components. The bolt is inserted through holes in the parts, and a nut is then torqued onto the threads to create a clamping force, holding the parts together.
Common Types of Bolts:
- Hex Bolts: The most common type, featuring a hexagonal head that is tightened with a wrench or socket. They are used in a wide variety of applications, from construction to machinery.
- Carriage Bolts: Characterized by a smooth, domed head and a square section underneath. The square section bites into the material (usually wood) to prevent the bolt from turning when the nut is tightened. They are often used for security and aesthetics.
- Eye Bolts: Have a loop or "eye" at one end instead of a standard head. They are used for attaching cables, ropes, or chains to a structure for lifting or securing loads.
- U-Bolts: Bent in the shape of the letter "U" with threads on both ends. They are commonly used to secure pipes or other round objects to a surface.
- Lag Bolts (Lag Screws): These are actually large wood screws with a hex head. They are used for fastening heavy lumber or attaching objects to wood.
2. Screws
Similar to bolts, screws are externally threaded fasteners. The primary difference is that screws are typically designed to be inserted into a pre-threaded hole or to create their own threads in the material (self-tapping). They are usually tightened by torquing the head with a screwdriver or a similar tool.
Common Types of Screws:
- Wood Screws: Designed with a coarse thread and a sharp point for easy penetration into wood. They often have an unthreaded shank below the head.
- Machine Screws: Have a finer, uniform thread and are designed to be used with a nut or into a tapped hole in metal. They come with various head types like flat, pan, or oval.
- Sheet Metal Screws: Have sharp threads that cut their own mating threads in sheet metal, plastic, or wood. They may have a pointed or flat tip.
- Drywall Screws: Feature a bugle head that sits flush with the drywall surface without tearing the paper, and coarse threads for gripping into wood studs.
- Self-Drilling Screws (TEK Screws): Have a drill-bit-like point that allows them to drill their own hole and tap their own threads in one operation, saving time.
3. Nuts
A nut is a type of fastener with a threaded hole. Nuts are almost always used in conjunction with a mating bolt to fasten multiple parts together. The two partners are kept together by a combination of their threads' friction, a slight stretching of the bolt, and compression of the parts to be held together.
Common Types of Nuts:
- Hex Nuts: The most common type of nut, used with a hex bolt or other threaded fastener.
- Lock Nuts: Designed to resist loosening under vibration and torque. Common types include nylon insert lock nuts (which have a nylon ring that grips the bolt threads) and prevailing torque lock nuts (which have a distorted thread).
- Wing Nuts: Have two large metal "wings" on the side, allowing them to be tightened and loosened by hand without tools.
- Cap Nuts (Acorn Nuts): Have a domed top that covers the end of the bolt for a finished appearance and to prevent snagging.
- Flange Nuts: Have a wide flange at one end that acts as an integrated washer to distribute the pressure of the nut over the part being secured.
4. Washers
A washer is a thin plate (typically disk-shaped) with a hole (typically in the middle) that is normally used to distribute the load of a threaded fastener, such as a bolt or nut. Other uses include acting as a spacer, spring (belleville washer, wave washer), wear pad, preload indicating device, locking device, and to reduce vibration (rubber washer).
Common Types of Washers:
- Flat Washers: The most common type, used to distribute the load of a threaded fastener and prevent damage to the surface being fixed.
- Split Lock Washers: Have a split in the ring and are bent into a helical shape. When tightened, the washer exerts a spring force that helps to prevent the fastener from loosening due to vibration.
- Toothed Lock Washers: Have serrated teeth on the internal or external diameter that bite into the bearing surface and the fastener head to prevent loosening.
- Fender Washers: Similar to flat washers but with a much larger outer diameter, used to spread the load over a wider area, often on thin or soft materials.
5. Anchors
An anchor is a type of fastener used to attach an object to a surface where a standard screw or bolt would not be sufficient, such as in drywall, concrete, brick, or stone. Anchors work by expanding within the base material to create a secure hold.
Common Types of Anchors:
- Drywall Anchors: Designed for use in hollow walls like drywall. Common types include plastic expansion anchors (which expand when a screw is driven into them) and toggle bolts (which have spring-loaded wings that open up behind the wall).
- Masonry/Concrete Anchors: Used for fastening to concrete, brick, or block. Common types include wedge anchors (which expand against the sides of a pre-drilled hole as the nut is tightened), sleeve anchors (similar to wedge anchors but with a sleeve that expands), and concrete screws (which cut their own threads into the concrete).
6. Rivets
A rivet is a permanent mechanical fastener. Before being installed, a rivet consists of a smooth cylindrical shaft with a head on one end. The end opposite to the head is called the tail. On installation, the rivet is placed in a punched or drilled hole, and the tail is upset, or bucked (i.e., deformed), so that it expands to about 1.5 times the original shaft diameter, holding the rivet in place.
Common Types of Rivets:
- Solid Rivets: One of the oldest and most reliable types of fasteners, used in applications where high strength is required, such as in aircraft frames and bridges.
- Blind Rivets (Pop Rivets): Can be installed from just one side of the workpiece, making them ideal for applications where access to the rear side is limited. They consist of a rivet body and a mandrel, which is pulled through the body to expand it and then snaps off.
7. Threaded Rods and Studs
Threaded rods and studs are similar fasteners used to connect objects over a distance. A threaded rod is a long rod that is threaded along its entire length. A stud is a shorter fastener that is threaded on both ends, often with an unthreaded section in the middle.
Common Uses:
- Hanging: Threaded rods are frequently used to hang pipes, ducts, and other equipment from ceilings.
- Anchoring: They can be cast into concrete foundations to provide an anchor point for structural members.
- Connecting: Studs are often used in automotive applications, such as securing a cylinder head to an engine block, where a bolt would be difficult to install.
Choosing the Right Fastener
Selecting the correct fastener for a job is critical. Factors to consider include:
- Material: What materials are you joining? (Wood, metal, plastic, concrete, etc.)
- Load: How much weight or force will the connection need to withstand?
- Environment: Will the fastener be exposed to moisture, chemicals, or extreme temperatures? (Stainless steel or galvanized fasteners are often required for outdoor or corrosive environments).
- Permanence: Do you need a permanent connection (like a rivet) or one that can be disassembled (like a bolt and nut)?
By understanding the different types of fasteners and their specific properties, you can ensure that your projects are built to last.
Mutual Screw is your fastener expert and happy to assist with any questions that you may have. Contact us today to learn more.