Machine Screw vs. Bolt: Pros, Cons, Types, & FAQ

They perform a similar function, but machine screws and bolts are not necessarily the same thing. Although they are both used as fasteners, machine screws tend to fasten into the material in which they are placed, while bolts pass through a hole and fasten into a bolt on the other side of the piece. With that said, there are some exceptions and there might be instances where machine screws fasten to a bolt. The two types of fasteners also tend to have different types of heads.

A machine screw will have a ridged head that can be used with a flat head screwdriver or Phillips screwdriver, while most bolts have hex heads that use a wrench. Again, though, there are exceptions.

Overview of Machine Screws

Although the term machine screw is often used to describe any screw, it really refers to a type of screw that is specifically used to hold together electrical and electronic components as well as machinery parts. These can be self-tapping or self-drilling and do not usually require the use of a bolt to form a connection because they use the thread that they tap into the work surface. They are also used in pre-threaded holes. While the screw itself does not thread or tap the hole, there is still no need for a bolt.

Applications

Machine screws are commonly used fasteners that are used in a host of different circumstances and for many different applications. They are found inside home appliances like washing machines and cookers. They are also found inside TVs, commonly used in computers, and they are also found in industrial and commercial machinery. They tend to be very strong to ensure that they offer a firm fastening.

Types of Machine Screw

There are many specialty types of machine screws available, which can include items like waterproof machine screws and galvanized screws, but the most common differences are as follows.

Coarse and Fine Thread

A coarse thread has 24 threads per inch while a thin thread has 32 threads per inch. The coarse thread does not offer as much strength or grip as a thin thread but should prove adequate in most home DIY jobs. A thin thread will usually be used where there is only room for a small screw, but it needs to be fixed firmly and tightly.

Machine Screw Heads

The other big difference in machine screw types is the head that they have.

Common head types include flathead or Phillips head, which work with the corresponding type of screwdriver. Square and star heads are also available and require a special type of driver to use.

Flat head screws screw right into the surface and their head is flush to the surface and does not protrude. Oval heads do sit close to the surface, but their rounded head protrudes out from flat surfaces slightly. Pan heads are designed to stick out from the surface, while truss heads also protrude but also have a wider surface area which means greater dispersal of the working load.

Overview of Bolts

Bolts serve a similar purpose to machine screws. They are used to fasten one piece to another or to connect two sheets together. They are typically passed through an unthreaded hole and connect to a bolt on the other side. The bolt is threaded, which means that the hole does not need to be. A washer may also be used to help ensure better grip and to ensure the working load is evenly spread around the surface near the bolt.

Applications

Bolts are usually used when two pieces of material need to be held together and they may have an unthreaded shank. They offer an extremely strong connection and are most often used in applications when strength is critical.

Types of Bolts

As with machine screws, there are many specialist bolts available that are designed for a very specific purpose.

Anchor bolts are added to concrete as it dries with the threaded section protruding so that a piece can be added with a bolt used to secure the two pieces.

Blind bolts are used where it is not possible to access both sides of the bolt, which is usually required to fasten and unfasten it.

With double bolts, both ends of the bolt are threaded, although each end might have a different type of thread and there is usually a central section that is not threaded.

Which Should You Use?

Whether you are better using a bolt or screw depends on how you will be using it. If you only have access to one side of the fastening, you will typically need to use a machine screw. If you have access to both sides of the pieces you are fastening together, a bolt may be the better choice. Another way to consider it is to look at the materials that you are connecting.

Which Is Best for Metal?

Typically, when fastening together two pieces of sheet metal, a bolt is the better choice. Not only is it stronger, but sheet metal is thin, and it won’t offer a strong enough thread for a screw to firmly hold on to. If you are fastening into solid or thicker metal, a specialist screw will likely be the better choice.

Which Should Be Used for Wood?

Wood can effectively be tapped and threaded, often without the need for even a pilot hole. In these cases, and especially if you do not have access to the back of the wood, a screw is your best option because you can screw this into the wood itself and it will anchor in position.

Which Will Cost More?

If you are only using one or a small handful of fasteners, the difference in price will amount to a couple of dollars at the most. If you are using hundreds of fasteners, the cost difference can be big. Machine screws tend to cost less than bolts but do shop around to ensure you get the best deal.

Conclusion

Machine screws and bolts are both types of fasteners that can be used to connect two or more items together. But, while machine screws are used to hold pieces of metal, machinery, and electrical and electronic components together, bolts are used when greater strength is required and when access to both sides of the fastening will be offered.

• See also: 7 types of hacksaw frames and blades

Featured Image Credit: (L) Piqsels | (R) Brett Hondow, Pixabay