Machine Screw Guide


What Is A Machine Screw?

Whether you are an experienced handyman or a homeowner working on a home improvement project with machinery, machine screws are probably on your list of materials to buy. This article is designed to help you learn more about what machine screws are so you pick the ideal products for your unique applications. You want to ensure optimal performance, which means you need to be sure you are using the right types of machine screws.

Machine screws are small, cylindrical pieces of metal with threading down the exterior surface, designed to hold two objects together. Not only are machine screws an integral part of the manufacturing industry but there are distinct advantages that set them apart from other types of screws.

As you’ll learn in this article, machine screws come in a variety of shapes, sizes, and materials. In fact, each machine screw has its own purpose and use.

Machine screws are used in many different projects and applications:

  • Building furniture
  • Industrial manufacturing
  • Engine installation
  • Constructing electronic devices
  • Large-scale equipment

These products are manufactured with higher standards and refined techniques to ensure superior quality, precision, and thread uniformity compared to other types of screws. Since machine screws are commonly used to secure metal components together in various machinery or for construction projects, they must perform with precision and reliability.




How To Pick the Right Machine Screw

As you learn more about machine screws, you will see that there are numerous head types, lengths, and sizes to choose from. These products are distinguished from other types of fasteners because they are designed with blunt ends and full threading. Machine screws tend to be smaller than bolts or screws in terms of both length and diameter, and they usually have flatter tips compared to other screw types with pointed designs.

Both coarse-threaded and fine-threaded versions are available, ensuring that machine screws can be used in a variety of applications. There are several important components to consider when choosing the right machine screws:

What Are Thread Size & Diameter?

Screw threads spiral down the surface so the screw can be driven into a surface or object. These external grooves dig out material so the screw can be inserted and secured in the desired location.

Machine screw sizing is measured with unified coarse pitch threads (UNC) or unified fine pitch threads (UNF) which indicates the number of threads in each inch of the screw. These measurements are essential to ensure uniformity between manufacturers. So, regardless of the manufacturer you choose, there is a pre-formed thread calculated to fit on the hole or nut where the machine screw will be placed.

Diameter can be measured in several ways, including major diameter, minor diameter, effective diameter, pitch flank, and crest.

What Size Machine Screw Do You Need?

Knowing how to read the sizing of a machine screw is necessary since most applications require a specific type. Generally, the nomenclature of a screw is formatted in this fashion: [Thread Diameter-Thread Pitch x Thread Length]. Now you must determine if your measurement system is Metric, or Standard SAE (Society of Automotive Engineers).

Here are 2 examples:

Standard SAE Machine Screw: #8-32 x 2”

The #8 displayed first is the nominal diameter, where #8 signifies 5/32 of an inch.

The -32 following indicates the thread pitch (distance between grooves) or 32 threads/inch.

The 2" is the final number and refers to the nominal length of the screw shaft.

Metric Machine Screw: M8-1.0 x 20mm

The M8 displayed first is the nominal diameter, where M8 signifies 8mm.

The -1.0 following indicates the thread pitch of 1.0 threads/mm.

The 20mm is the final number and refers to the nominal length of the screw shaft.


This rule applies to all standard and metric screws; however, some exceptions may vary in size and structural dimensions.




What Are The Different Types Of Machine Screws?

 Sizing Chart:

Standard Nominal Diameters:

Metric Nominal Diameters:

Machine Screw Heads

Machine screws not only come with different lengths and threads, but the type of head is also key when choosing products. Most machine screws have flat or slotted heads but can also come with hex, pan, or oval heads. You’ll need to consider how the machine screw is being placed to determine the ideal head for your application.

Round Head

The Round Head machine screw is often used in machinery. This design has a unique, large dome-shaped head, so you have extra grip, making it easier to hold and turn the screw without slipping. Not only is the roundhead convenient and practical, but it also looks good when the screw is in place. Whether you’re looking to assemble complex machinery or small crafts, this type of screw delivers reliable performance and a stylish finish.

Flat Head

If you need a flush finish, then a flathead machine screw (also known as a countersunk screw) is an excellent option to consider. These screws feature a flattened top with a countersunk underneath silhouette, so they fit neatly into panels and components without any protrusion. These screws are often used on handrails, furniture, and lighting fixtures, offering a reliable fastening solution where a flush finish is preferred.

Truss Head

Truss Head screws are designed for a secure fastening that stands out. This type of screw has a unique, mushroom-shaped head protruding farther than other standard screw heads, making it a great choice when visuals are necessary. Whether working on an artistic project or creating something more utilitarian, truss head screws can lend just the look you desire with the necessary function and stability.

Cheese Head

Cheese head screws offer greater strength and durability compared to traditional round head screws, thanks to their unique shape. When you are looking at the screw from above, you see a flat-topped, cylindrical head with quite a bit of depth compared to other types of screws. The flat disc top is ideal for slot drives since it provides an accurate driving capacity. This type of screw is often used for assembling appliances, automotive parts, and fixing electrical components.

Hex Head

Hex head machine screws, commonly known as set screws, are similar to traditional bolts in both shape and usage. Their distinct six-sided head, or hexagon shape, makes them easily recognizable. These fasteners can be used in a variety of applications where a wrench or spanner is necessary for extra torque. However, they are also frequently designed with a recessed drive socket so that installation can be done with a more traditional screw-driving tool as well.

Pan Head

Pan head screws are the perfect choice for both industrial and automotive applications. They are designed with a wide, circular head and a flat bearing surface, offering secure mounting and holding power. The shape of the head can be either flat or slightly domed, depending on your needs. One notable safety benefit is that pan head screws are made with no sharp edges. The smooth, minimalistic surface offers an aesthetic appeal, making them popular in various applications.

Oval Head

Oval head machine screws feature a rounded top surface and conical bearing surface and provide an aesthetic appeal because they are less noticeable. They are commonly found in switch covers and other construction projects. Although oval-head machine screws do not countersink as neatly as flat-head machine screws, they provide a middle ground between standard pan heads and flat heads – giving you the aesthetics and functionality in one.

Fillister Head

The Fillister Head screw is a great choice for precision instruments and mechanical assemblies. It is designed with a convex top and flat bearing surface, minimizing the risk of loosening over time due to vibrations and impact. Additionally, its oversized head gives it greater height than other kinds of head screws, such as the pan and cheese heads - perfect for counterbored holes that require more protection from the screwdriver. Depending on your application, this type of head screw is available with both a slotted or Phillips drive.

Socket Head: