Grub Screw vs. Set Screw: Facts, Differences & FAQ

If you have ever dabbled in at-home mechanic work or certain types of construction, you might have come across the terms grub screw and set screw. Set screws are special types of screws used for specific purposes. If you do not know what a set screw is, it is likely that you have never intentionally used one. They are not the same as common wood screws and drywall screws.

What exactly are grub screws and set screws? Are they the same thing, and are they interchangeable? In order to ensure that you use the correct screw for the correct purpose, it is important to know the answers to these questions. This short overview will supply the answers. By the end, there should be no confusion about what is and is not a set screw.

Set Screw Overview

Set screws are specific types of screws that have no head and are threaded along their entire length. They differ from normal screws in that they are designed to hold two loose components together and sit flush within a surface. Regular screws are defined by their head. There are flathead screws, hex head screws, and others. Set screws have no head at all.

Set screws sink into a predrilled hole and work to create enough compression force to hold things together. Set screws are special because they have no overhanging parts, like a head, that could interfere with the movements or operation of machinery. That is why set screws are most often found used in moving parts, especially machinery and engines. You can identify a set screw by the fact that they are threaded along their entire length and are often small and uniform in shape.

Are Grub Screws the Same as Set Screws?

Grub screw is simply another term for a set screw. Many people use the terms grub screw and set screw interchangeably. The term grub screw comes from the fact that a set screw burrows into a surface and becomes flush, almost vanishing. It is similar to that of a grub that burrows in the ground. The split between the grub screw and the set screw is based largely on a split in the English language. The set screw and grub screw are divided along British and American lines. British English and American English are different dialects.

American English calls these screws set screws, while British English refers to them mainly as grub screws. If you search grub screw on the internet, you are likely to come across British websites and British sources. If you search set screw, you will likely come across American websites and American sources.

Some people think that grub screws are set screws that sit entirely within the hole, but that is usually a characteristic of all set screws. For the vast majority of purposes, it is safe to use these two terms interchangeably. Other names for set screws include socket screws, setscrews, and grub screws. All of these terms refer to one another equally.

What Are These Screws Used For?

The most common use for a set screw is to hold two components together. Usually, this means holding one component inside of another. These components are usually moving. Many industrial machines and mechanical engines have moving parts that require set screws to hold them together in such a way that it does not impede the free flow of the machine.

For example, holding two rotating parts within one another so that they can both rotate. This would be impossible if using a bolt or regular screw with a large head. Sockets, sprockets, pulleys, wheels, and gears are all common assemblies that feature set screws because of their unique characteristics. These are also common parts of old car engines, which is why set screws are often stumbled upon during mechanical work in the garage.

Another common place to find set screws around the house is within doorknobs. Doorknobs also have rotating pieces that need to move smoothly, efficiently, and consistently. Doorknobs can’t have extruding parts that could impair the movement of the knob and lock someone out of a room.

Set Screws vs. Bolts

Another source of confusion is the separation between set screws and bolts. Bolts are also used to hold two components together. However, bolts keep tension by using nuts and washers. The threaded end of a bolt is secured with a nut which then pushes the bolt and holds it into place. A set screw is designed to hold the components in place without the use of any nuts or washers. Nuts and washers could be hindrances to the movement and function of a finely tuned machine. Machines work best when they have fewer components, especially extruding components. That is why set screws are often used in place of bolts to secure things that move.

Conclusion

Set screws and grub screws are terms for the same type of fastener. These screws are special and feature no heads and are fully threaded. They are commonly found in machinery where regular screws or bolts would prevent moving parts from functioning properly. If you see the term set screw or grub screw, know that they are referring to the same thing and can be safely used interchangeably. Americans are more likely to use the term set screw, while the British are more likely to use the term grub screw.

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