Machine Screws; Standards, Applications, Specifications

Flat head machine screws.
Image Source: Flickr.

Screws are very important elements in machine designs. They have a very big job in lots of kinds of machinery. One of these kinds is machine screws. We give detailed information about them. You can find information about these machine elements;

  • What is a machine screw?
  • What are the types of it?
  • How do produce them? What are the materials?
  • How do show machine screws in technical drawings?
  • Screw drive types of these screws
  • Advantages and disadvantages of them.
  • FAQs

So, you can find lots of information about them in this guide.

What is Machine Screw?

Machine screws are a type of screws that we use in different kinds of assembly applications. We use them to assemble two or three planes for each other. They are very like cap screws. But they are smaller than the cap screws. And also, the thread geometry starts from right below the head, unlike cap screws.

They have advantages and disadvantages over other types of assembly operations. So, these screws can find various kinds of applications themselves.

For all types of machine screws, there are slotted and recessed head types.

Types of Machine Screws

In general, there are four types of heads in machine screws. Each of them is used in different kinds of assemblies.

Round Head

Round head machine screw.
Image Source: Home Depot

This is the first type and the most common type of these screws. As you understand from its name, the head shape of these screws is semi-circular. The height of the round head cap is the 3/4 times diameter of the screw. Also, screw drive clearance is 0.25 times of screw diameter. And also, the deepness of screw drive clearance is 0.5 timed diameter.

The only disadvantage of the round head, there will be protrusions of the screw heads on the surface of the machine.

Flat Head

Also, this is a very common type of them. As you understand from its name, the top of the screw is flat. The total thickness of the hard of the flat head machine screw is 0.25 times the diameter. The deepness of the screw drive clearance is 0.25 times the diameter. Also, the clearance of the screw drive is 0.25 times the diameter.

The angular aperture of the flat head screw is 80°.

The most important advantage of the flat head screws is there is no protrusion on the surface. All the screw is buried inside the work part.

Oval Head

Oval head machine screw.
Image Source: Ingeniosivtual.com

An oval head machine screw is like a round head screw. But the roundness is more smooth in these types of screws. The total ovalness of the top of the screw head is 80°. The total height of the screw cap is 0.5 times the diameter. The screw clearance dimensions are the same as the flat head screw.

There is very little protrusion on the surface if we attach an oval head machine screw. This is because of the ovalness.

Fillister Head

Fillister head.
Image Source: Fasteners.eu.

This is the fourth type of screw. The cap of the fillister type is like an oval head, but the sides are parallel. And it is not buried inside the workpiece. The total span of the fillister head is 1.5 times the diameter of the screw. The thickness of the fillister head is 3/5 times of the screw cap. Also, the deepness of the screw drives clearance 2/5 times the diameter. And also, the clearance of the screw drive is 0.5 times the diameter.

Like the round head, there is a protrusion on the surface of the workpiece because of the cap.

Manufacturing and Materials of Machine Screws

The manufacturing of machine screws is the same as other types of screws. The raw body and the cap are obtained with metal shaping processes such as hot rolling. And then, the thread geometries are obtained with machining operations such as turning. 

There are various kinds of materials to produce them for different purposes.

  • Steel: Steel is one of the most common materials that we use to produce these screws. Especially stainless steels are very important in the production of high-strength machine screws.
  • Brass: Also for high strength and corrosion-resistant applications, brass is a very common material in the production of them.

In general, they produce the standard machine screw as not heat treated and also bright thread finish. Unlike other screw types, chamfer geometries are not used at the caps of these screw types.

Specifying Machine Screws in Engineering Drawings

Also for these screws, there are standards that we need to obey. According to these standards, they produce different kinds of these screws. And also, we need to specify them on technical drawings according to standards. Here you can find examples of how to define them exactly for US and metric standards.

US Machine Screw Notes

For example;

  • NO.10(.1800) – 20 NF-3 X 5/6 FILLISTER HEAD MACHINE SCREW

If we take a look at this note, we can say that the diameter of the machine screw is .18 inches. Also, the type of the thread class is 20 NF-3 And the length of the screw is 5/6 inches. And then the type of the screw is fillister head machine screw.

Furthermore, we can show the type of screw in abbreviated form. For example, we can write FILH MSCR instead of the long name above.

Metric Machine Screw Notes

In the metric system, it is very simple to show the screw notes. Take a look at the example below;

  • M10 X 1.5 X 30 X SLOTTED PAN HEAD MACHINE SCREW

We can understand that the diameter of this metric screw is 10 millimeters. And the metric thread type is 1.5. And also the length of this screw is 30 millimeters. The type of this screw is pan head and it is slotted type.

Screw Drive Types on Machine Screw Heads

We are using standard screw drivers in the assembly and disassembly of the machine screw heads. There are various shapes on the caps of the screws. These shapes are valid for all other types of screws. So, you can find different applications of these different screw drive shapes.

Image Source: FREDERICK E. GIESECKE, SHAWNA LOCKHART, Technical Drawing With Engineering Graphics 15th Ed., Pearson, Pg.619
  • Slotted Screw Drive: This is the most common one. There is a straight clearance on the top of the cap. We can use straight screwdrivers to detach or attach these types.
  • Phillips Type: There is an ‘X’ type clearance on the cap of the machine screw. This is also a very common type of screw drive. The advantage of this type of screw drive is it prevents the over-tightening problem.
  • Pozidriv Screw Drive: This type is somewhat similar to the Phillips type. But you can see extra thin clearances also. These extra thin clearances provide more torque application capability on machine screws.
  • Hex Screw Drive: This is one of the most common types of screw drive. In general, we use Allen keys to attach and detach these types of screw drives. Also, the general advantage of the hex screw drive is tooling expenses are very low.

Other Important Types

  • Hexalobular: This is the six-point start design of the screw drive type. In this type, there is much better contact between the screwdriver and the machine screw. This provides better contact for higher torques. Also, they call Torx head screwdrivers.
  • Security T: This is a very special design of a screwdriver head. It resembles hexalobular but there is a protrusion at the center. You need to have a special tool to detach it. So, it provides extra security for the machinery. For example, you can barely detach Phillips type or Hex screw type with a straight screwdriver. But, you can not detach Security T with other screwdrivers.
  • Double Square: The shape of this screwdriver type of 8-point star. Also, you can see that two squares are placed on each other. The main advantage of this kind of screwdriver type is, that you can insert the tool very easily.
  • Japanese Industrial Standard(JIS): This is a very like Phillips screw drive type. But the only difference is there is a minimal slot on the ‘X’ shape.

Also, other types of screw drive shapes are available for different special applications.

Applications that Machine Screws are Used

Because of their advantages and differences, machine screws can find different kinds of applications themselves. Check the application example below that these screws are used.

Firearms

Firearms have lots of kinds of parts that need to be attached. So, they use small machine screws in the assembly of the parts of the firearms. Because they are very tight and easy to disassemble in the required times.

Jigs in Machining

Jigs are very important parts of manufacturing processes. They provide better placing work parts and tools for machining operations. In the assembly of jigs, we are using different types of machine screws. Because we can use these screws in disassemble the jig continuously. Also, they provide extra rigidity which is very important in the jigs.

Fixtures and Dies

We use dies and fixtures of dies in the metal casting processes. Also, rigidity is very important in these systems. So, we use them in different sizes to obtain rigid fixtures and die systems. We also close and open dies lots of times. So, machine screws can be used in these systems.

Electrical Connections

In electrical connections, these screws are very common. Also, we use smaller machine screws in the connection of electrical terminals in lots of kinds of devices.

Advantages and Disadvantages of Machine Screws

Like other machine elements, there are advantages and disadvantages of machine screws. Because of these advantages, we use them in different applications. Also, we need to consider the disadvantages of the design phase.

Advantages

  • In general, we use these screws in heavy-duty and industrial-level applications. This is because of their application ease and mechanical strength.
  • They are smaller than the other fastener types. This is an important fact that they will occupy lower space.
  • The threads of machine screws start from below the cap of the screw. This provides more rigid applications.
  • Mechanical strength is the most important advantage of the machine screws.
  • In general, we use these screws in the assembly of heavy metal parts. Also, we use them in small assemblies such as electrical connections.

Disadvantages

So, we need to consider these disadvantages of machine screws in mechanical design. 

  • The most important disadvantage of these screws is, that we need to create holes to attach them. So, we need to drill the work part which can affect the mechanical stability.
  • Accumulating stress can be a problematic issue for screws. Shear stresses can be a problematic issue. For example, in welding operations, the stresses spread along the weld seam. This is a less dangerous state of stress.

Conclusion

Machine screws are very important in the design of different kinds of engineering systems. Also, there are various sizes and types of these screws that we can use.

Furthermore, there are different advantages and disadvantages of machine screws that we need to consider. While you are selecting a proper fastener, you need to know the general advantages and disadvantages of these screws.

You need to specify and note properly which sizes and types of machine screws you used in your system. Because it is very important for the production phase.

Because of their different advantages and disadvantages, there are lots of kinds of applications for these screws. There are very big and heavy duty applications and small loads applications of these screw types.

Also, you can select a type of screw drive mechanism according to your application.

Finally, do not forget to leave your comments and questions below about this topic.

Your precious feedbacks are very important to us.

FAQs About Machine Screws

Can be machine screws used on woods?

Yes, there are types of these screws that we can use on the wooden parts. Because they are very efficient to combine the wooden parts efficiently.

Can be machine screws used on plastics?

Also yes, we can use them on plastic parts. But we need to give special attention to the assembly of these screws. Licking can be a problem in the machine screw application on plastics. 

What is a machine screw?

A machine screw is a type of screw that has a cap. The threads start right below the cap and the edge of these screws is blunt. Also, these screws are smaller than the other types of screws. These are the main characteristics of these screws.

How to use machine screws? 

It is very simple. We need to open proper holes to attach these screws. And we need to attach these threads of screws to these holes. So, we can obtain very rigid structures.

What are the machine screw sizes?

There are various sizes of machine screws. Both in metric and US types of machine screws, varioıs sizes are starting from millimeters to several centimeters.

Do machine screws need nuts?

n general applications, we are not using nuts with machine screws. Because the threads of these screws are attached to the work part itself. There is a strict assembly between the threads and the work parts.

Also, you can check these other useful posts about engineering below.

Explanation of Thread Rolling Processes

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Lubrication Types of Machinery Parts

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