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.
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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.
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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:
A socket head has a recessed hexagonal design, allowing for use with a corresponding socket driver or wrench to loosen or tighten the screw. This design offers several benefits over other types of screw heads, such as improving grip to minimize slipping. The shape of the screw head is ideal for machines that require a high torque. Additionally, these screws are useful in tight spaces where it would be challenging to access other types of screw heads.
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What Machine Screw Drive Type Do You Need?
The most common drive types include:
Slotted: A straight, single socket that runs across the head of the machine screw, so it can be fastened with a flathead screwdriver.
Phillips: This type of machine screw features an X-shaped socket in its head, providing slightly more potential torque than standard slots.
Torx (also known as Hexalobular Recess or Star Drive): This design is characterized by its six-pointed star-shaped socket and requires a torx or star bit for installation.
Hex Head: Hex head screws feature a six-sided design and are commonly recommended when high torque is required because the hexagonal shape allows a tighter drip for the wrench.
Socket Head: These screws allow precise tightening and high torque, making them an excellent choice for machinery, construction, woodworking, and automotive applications.
Machine Screw Materials and Finishes
It’s important to consider the type of screw materials and finishes that will suit your application. The purpose of the machine screw will influence which material and finish you need. So, the best solution is to refer to the machine instructions or manufacturing information for recommendations.
Materials matter because they are often subjected to high temperatures and pressure, so you need a screw that will hold up under a high-stress environment. The two most common finishes available are zinc-plated and stainless steel. You can also find machine screws made with other materials such as black oxide, black zinc, and nickel.
Steel
Steel is the most common material used for manufacturing machine screws and other types of screws, due to the strength and durability steel offers. Plain steel is available, or many of these products have a surface treatment such as zinc plating, chrome plating, or galvanizing. Steel screws come in four grades: 2, 5, 8, and alloy steel. Typically, screws with grades 2, 5, and 8 are yellow or blue in color because they are usually plated with zinc to improve corrosion resistance.
Stainless Steel
Stainless steel is a preferred material for machine screws due to its strength, durability, and resistance to rust and corrosion. The different varieties of stainless steel include 18-8, 316, 410, and Grade 10. Quality stainless steel contains chromium, which helps maintain the properties despite extreme temperatures and weather conditions – creating the desired rust-resisting features. So, stainless steel materials are excellent for many machines, providing superior protection against wear and tear.
Brass
Brass machine screws are an ideal choice where corrosion prevention is important. Brass machine screws often go hand-in-hand with sturdy solid brass nuts; these two components will provide unbeatable protection against tarnishing regardless of environmental conditions. Unlike steel, which will corrode and rust over time in certain environments, brass is far more durable and won't corrode as easily. This makes them a great choice when corrosion is a concern.
Nylon
Nylon is a preferred material for machine screws and other types of applications due to its high tensile strength and superior wear resistance. Not only is it rust-proof and non-conductive, but nylon is a cost-effective choice that also provides the corrosion resistance necessary in many situations. Nylon screws are often used for electronic work since they don’t conduct electricity.
Finishes
In addition to picking the screw material, consider how the finish will impact long-term performance. Available finishes include:
Zinc-Plated machine screws provide both an aesthetically pleasing and corrosion-resistant finish, making them great for outside applications.
Stainless Steel is a tough yet high-quality material resistant to corrosion. It won't oxidize or degrade when exposed to rain, humidity, and other outdoor elements, therefore offering longer-lasting durability compared to other materials.
Black Oxide is a typical finish used to enhance the look of machine screws and other hardware. Not only are there aesthetic benefits, but this finish also adds an additional layer of protection against natural elements that could damage otherwise exposed metal surfaces.
Black Zinc is an extremely popular finish for machine screws because it helps protect the underlying element against galling (damage caused by physical abrasion or electrolytic contact). It’s a great finish for machine screws that need to resist corrosion in wet environments or harsh weather conditions.
Nickel is another finish that withstands corrosion, erosion, and abrasion. Since nickel plating doesn’t chip, it is ideal for applications when there will likely be friction or wear.
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Picking the Right Machine Screw for Your Project
In conclusion, there are many factors to consider when picking a machine screw. These details make a difference in the durability and performance of the screw, so ensure that you've considered all the necessary options for your application. Not only do you need to think about the size, thread, and diameter of the screw, but the screw's material and finishes will also impact the long-term performance.