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Bolt vs Screw: What’s The Difference?

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People commonly refer to fastening hardware with external threading as both screws and bolts. However, using the terms interchangeably is a common mistake. Despite their similarities, bolts and screws are different types of fasteners used for different applications.

We’re here to discuss the difference between bolts and screws, as well as the different types of each fastener category, their unique advantages, and their drawbacks.

When to Use a Bolt vs a Screw

There aren’t any officially defined differences between bolts and screws, as they’re both externally threaded fasteners typically made of steel or carbon steel. However, they can be defined and differentiated by their respective applications.

Bolts are externally threaded fasteners used with suitable and matching internally threaded fasteners, such as nuts, that are used to couple two or more unthreaded parts and components together. This means that the bolt only passes through through-holes in coupling elements.

Regardless of the type of bolt used, its own threads aren’t interfacing with the coupling elements in any way. Instead, the threaded shank interfaces with the internal threads of a suitable nut fastener, such as a hex nut.

Screws, on the other hand, have similar characterizations as the bolt. They’re also externally threaded components used to couple two or more parts or components together. However, unlike bolts, screws don’t require a separate fastener to hold the parts tightly.

Instead, they’re coupled with a tapped hole or create their own threads in pre-drilled holes during fastening, as is the case with self-tapping screws. This applicational division between bolts and screws carries another implication; bolts can be larger in size to achieve higher load-carrying capacities. In contrast, the screws are generally employed for relatively small load-carrying applications, such as in small machining or woodworking applications.

Types of Bolts

There are several different types of bolts, distinguishable by their design, installation, and application. They’re almost exclusively used in conjunction with nuts to couple two or more components together, in which case the shank of the bolt acts as a dowel pin between coupled components.

Hex Bolts

Hex bolts, also known as hexagonal bolts, are the most commonly used bolt in construction and machining due to their high strength and durability. The hex head allows for fastening using wrenches, pliers, sockets, or even grips.

Carriage Bolts

Carriage bolts, or coach bolts, are more commonly used in woodworking applications that demand a smoother finish. Their specific design prevents the bolt from turning when the nut is tightened, while the rounded head provides a finished appearance once installed.

Anchor Bolts

Anchor bolts are most commonly used in concrete and masonry applications which require a high degree of strength. The bolt features a threaded end and a cone-shaped expansion sleeve that wedges against the side of the hole the bolt’s inserted.

Types of Screws

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Screws don’t require fastening nuts, as their threads interface with the threads in the elements they’re fastening. Here’s a list of different screw types:

Wood Screws

Wood screws are designed for use on wood and other softer materials. They typically have a sharp point and a coarse thread that grips the wood and prevents the screw from slipping. It’s important to note that some installations might require that you drill a pilot hole in the wood material before driving the screw using a screwdriver.

Sheet Metal Screw

Sheet metal screws are specifically designed for fastening sheet metal or other thinner components, such as plastic or fiberglass. They also have a sharp point like the wood screws, but their thread is much finer compared to the coarse threads found in wood screws.

Machine Screws

Machine screws can resemble bolts to an untrained eye. These have a flat-ended shank with a fine thread, just like bolts do. However, unlike bolts, most machine screws have the full length of their shank threaded.

Additionally, they interface with the components being attached. This means that they’re actually installed in pre-drilled threaded holes in components, or elements joined together.

Self-tapping Screws

Self-tapping or self-drilling screws cut their own threads as they’re being screwed into the material. They’re commonly used in applications involving wood, plastic, and thin metal sheets.

Lag Screws

Often referred to as lag bolts, lag screws are very similar to bolts, as they have a hexagonal head and a long grip length (the unthreaded section of the shank), but instead of fine threading, their thread is rather wide. They’re typically used in heavy-duty applications such as construction and woodworking.

Drywall Screws

These fasteners are specifically designed to fasten into drywall or other types of gypsum board. They’re very similar to wood screws; however, they typically have finer threads, though coarse-thread variants also exist that are made of harder materials.

Types of Screw Heads

Screws are far more versatile than bolts and have a wider range of head designs.

Flat Head

Flathead or slot head screws typically have a single slot across their top to accommodate a flathead or slot screwdriver. The shape of the head can be a round head, pan head, oval head, truss head, and many similar shapes.

Phillips Head

Phillips head screws have a cross-shaped recess on top, which allows for high-torque applications such as electronics or woodworking.

Torx Head

Torx head screws have a six-pointed star-shaped recess on top. They are commonly used in electronics, machinery, and automotive applications, which require a high-strength fastener.

Socket Head

Socket heads, or Allen screws, have a recessed hexagonal socket on top, making them suitable for applications that require a high-strength fastener that’s flush with the material surface.

Find Industrial Screws and Bolts

Screw and bolt materials are intricate and essential. The type, length, head type, and diameter matter a lot when trying to find the right component for your specific application. Find steel, stainless steel, or Northwestern screws and bolts at Reid Supply.