Your guide to machine screws

With so many types of screws available for various industries, jobs, and DIY tasks, it’s hard to imagine how this one small fixture can have so many different designs and purposes. 

While the machine screw is fairly easy to figure out (they’re designed to be used for machinery), the term ‘machine screw’ actually covers a wide range of screw types, and their purpose is a bit more multifaceted. 

That means there is no single type of machine fastener, which is where things can get confusing when you’re trying to buy the right one for your project. Luckily for you, we’ve created a quick and easy guide that answers the question ‘what are machine screws’, so you’re no longer left in the dark.

Do you need screws for your project fast? We sell a range of fixings, from wood screws to concrete screws, offering fast and efficient delivery.

What are machine screws?

While yes, machine screws are designed to join different types of metal machinery, such as in industrial or construction work, they aren’t specifically made for machines only. 

In fact, the term ‘machine screw’ just refers to screws that are smaller than 0.75 or less in diameter. These screws usually feature a fully threaded design for use in a tapped hole (an internal thread) or paired with a nut. They can also be coarse-threaded or fine-threaded, depending on their use, and are available in a range of head types and metals.

You’ll see them across metalwork, electrical fittings, appliances and general assembly where parts need a consistent clamp along the full shank. While many screws feature a pointed edge for piercing into materials, machine screws have a blunt edge or flat tip, so they rely on an existing thread or a nut to remain in place.

Since they’re often used for joining machinery, they feature a robust design, offering exceptional strength, durability, thread uniformity, and precision. 

The different types of machine screws

When it comes to the different types of machine screws, there are three things we need to look at: the head shape, the drive, and the material/finish the screw is made from.

There’s also a fourth component, thread form, which decides how it connects with a nut or tapped hole. We’ll quickly run through each one below so you get a better gist before choosing the right machine screw for your project.

Common head shapes 

  • Pan head: The everyday choice for panels, brackets and electrical faceplates, these screws have a slightly domed and broad head that helps to spread the load across the surface.
  • Button and cheese heads: Similar to round head screws, button and cheese head screws provide a lower profile while leaving the head slightly visible. Button heads tend to be rounded with a wide bearing surface, while cheese heads are more cylindrical and compact, useful where you’re tight on space.
  • Truss/round head: Round head machine screws are another shape that works well to spread the load, making sure the surface doesn’t break. Many use these for thin sheets of plastic and metal, or when they are fixing a plate or a stra,p and want to avoid pull-through without using a penny washer.
  • Countersunk (flat) head: These are designed to sit flush into the surface once the hole is countersunk, providing a neat and unobtrusive look. For this reason, they’re popular for tasks where a tidy appearance and convenience matter, like hinges and cover plates.

Drive types 

Pozi and Philips drives are commonly found on UK machine screws, since they’re versatile and offer excellent longevity and better torque. Since they have an X-shaped recess, they can be used with screwdrivers and drills and provide a better grip.

However, Philips heads are more prone to cam-out than Pozi heads when used at a higher torque, so pick a Philips head machine screw when you don’t need heavy drive force for the installation. 

If you want something simple and classic, then a slotted head screw is the best choice. Be wary that they are prone to slipping, though, and only use them for very basic fittings. If you’re working with machine screws with button or low-profile heads, a hex socket (Allen) drive keeps the head compact while still allowing a good amount of torque.

Materials and finishes

Machine screws come in a range of finishes and metals, depending on their intended use. Most builders choose A2 (304) stainless steel screws for a wide range of construction projects since they offer excellent resistance to rust and corrosion. 

It’s a great choice for most indoor and outdoor jobs since it can withstand harsh weather conditions without faltering. For coastal sites or areas with chemical exposure, A4 (316) stainless is a great choice, as it offers stronger corrosion resistance. 

If weight is a concern, aluminium machine screws offer good resistance to rust, but they’re not as durable as stainless steel. Brass and Nylon machine screws are also popular for electronic fittings, as they’re non-magnetic. Nylon, in particular, is great for applications where insulation, low weight, and non-marring contact are important.

What are machine screws used for?

Here is a non-exhaustive list of when machine screws will more than likely come in handy: 

  • Electronic devices
  • Tool assembly 
  • Vehicles 
  • Large-scale industrial equipment 
  • HVAC and ducting
  • Furniture hardware

How to read an M-spec (M3, M4, M5…)

The metric scale is the standard measuring system used to determine the diameter of a machine screw. You’ll see the letter M followed by a number; the higher the number, the larger the diameter of the screw.

When you see M5 × 20, the M tells you it’s a metric thread; 5 is the nominal thread diameter in millimetres, and 20 is the length in millimetres. If there’s no pitch shown, read it as the default (coarse) pitch for that diameter.

The head also determines how length is measured. For example, since the head sits on top of the surface with pan, button, cheese and truss head screws, you measure from under the head to the tip. For countersunk machine screws, you measure the overall length from the top of the head to the tip, because the head is designed to sit flush in a countersunk seat.

When it comes to threads, coarse threads are ideal for most general applications and are easier to work with, while fine threads are reserved for more complicated and specialised equipment. 

Why Buy Machine Screws from Efixings?

Are you looking for high-quality screws for your next project?

At Efixings, we sell a variety of fully threaded machine screws for professional and DIY projects, available in different head types and finishes. Each one is designed to offer a precise and robust installation for a long-lasting hold. 

Browse our range today to find reliable solutions for your next project.

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