What Are Thread Rolling Screws And When Should You Use Them?
What Are Thread Rolling Screws?
Thread Rolling Screws - also known as Thread Forming Screws - are a type of fastener designed to create secure connections within metal, plastic and wooden assemblies.
Essentially, a Thread Rolling Screw is similar to a Self-Tapping Screw, but with a finer pitch and a thread form that is closer to that of a machine screw.
With a trilobular shaped thread, and a slight taper to the end of the fastener, these components do not require a pre-tapped hole. Instead, Thread Rolling Screws have self forming properties and will create their own threads as they are driven into a pre-drilled hole.
The trilobular shape of a Thread Rolling Screw makes it ideal to do just that, providing areas of relief which prevent the threads from cracking from the cutting pressure.
Similarly, with a larger minor diameter than comparable Self-Tapping Screws, Thread Forming Screws can handle the higher installation torque that is necessary for harder assemblies.
When inserted, the screw will begin to deform the material within the assembly, forcing it outwards. This is different to that of Self Tapping Screws, which ‘cut’ and remove material to create a thread.
Typically, as the material is reshaped to fit tightly around the screw, the threads that are formed by Thread Rolling fasteners can be stronger than those created by Self-Tapping Screws.
As a result, these components are less likely to loosen over time, making them ideal for applications where a firm and reliable connection is essential - such as manufacturing where loose components can have disastrous effects.
Accu’s Thread Forming Screws are available in A2 Stainless Steel with the added option for Chemical Blackening.
Is Thread Rolling The Same As Thread Forming?
Thread Rolling and Thread Forming are both terms that can be used to describe how a thread profile is formed, or more specifically, how the helical ridges are created on the component itself.
Though they have minor differences, the terms ‘Thread Rolling’ and ‘Thread Forming’, refer to the same thing and can be used interchangeably.
Thread manufacturing is not a one-size-fits-all and, with such a wide range of threaded nuts, bolts and screws, multiple manufacturing methods are necessary.
Thread Rolling, or Thread Forming, is one method for doing this whereby Thread Rolls are used to create external threads on mass produced components, such as those on a machine screw or bolt.
During this non-subtractive process, the component is placed under pressure, with a form that shapes the exterior of the material into a thread.
These forms are often in the shape of a pair of Grooved wheels, or Grooved plates.
The fastener is placed between these tools and pressure is applied, causing the fastener to roll between the tools and form a continuous thread.
By comparison, the Thread Cutting is used to create internal threads - as seen on nuts. This is done with a Thread Cutting insert or tap, which is inserted into the material to create the internal threading.
Both of these operations are cold working processes, meaning that they are performed at room temperature.
What Is The Difference Between Rolling Threads And A Thread Rolling Screw?
Whilst ‘Thread Rolling’ refers to the process of forming an external thread, this should not be confused with Thread Rolling Screws, themselves.
A Thread Rolling Screw is not necessarily a screw that’s threads were formed by Thread Rolls, though they can be. Rather, the ‘Thread Rolling’ properties of the screw define how the component behaves when installed into an assembly.
In essence, a ‘Thread Rolled’ Screw is a fastener that is manufactured using the process of Thread Rolling whereas a ‘Thread Rolling Screw’ is a fastener specially designed to use a non-subtractive, deforming method to form a thread in an assembly.
To learn more about the methods used to create the threads of a component head to our article ‘Rolled Thread vs Cut Thread - The Differences And Benefits Of Each Thread Type’.
Are Thread Rolling Screws Better Than Self-Tapping Screws?
Thread Rolling Screws are often referred to as a Self-Tapping Screw and, though they are similar in theory, they are not the same.
This is not to say that Thread Forming Screws are better than Self-Tapping Screws, but rather, they each have characteristics that are suited for use in different types of applications.
To deem one better than the other you must first consider the material requirements of the project. Though, it should be noted that - since they are designed to create their own threads - both Thread Rolling Screws and Self-Tapping Screws should be installed into malleable materials.
As mentioned previously, a Thread Rolling Screw creates its threads by deforming and compressing the assembly material, whilst a Self-Tapping Screw will cut and remove the material instead.
Typically, Self-Tapping Screws are easier to install due to their lower driving torque. They are also more versatile and can also be used in a wider range of applications and materials including plastic, wood and thin metal sheets.
With a deeper thread, Self-Tapping Screws have more ‘bite’ which is necessary for a secure hold in softer materials such as wood.
By comparison, Thread Rolling Screws are better suited to higher grades of aluminium and similar materials. Though they can be used in thinner sheet metal applications, this is not often the case due to their higher expense.
As previously mentioned, to form or cut a thread, both Self Tapping Screws and Thread Forming Screws must be inserted into malleable materials. If the assembly material is harder than the material of the screw, it will not be able to tap or form a thread. Instead, the threads of the screw will begin to wear and strip.
This is why standard Self-Tapping Screws are not recommended for harder metal assemblies. Where the design of a Thread Rolling Screw makes it suitable to penetrate higher grades of aluminium, such as the trilobular shaped thread or the fact that they have a larger minor diameter, Self-Tapping Screws do not have these features.
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Another reason that standard Self-Tapping Screws are not recommended for harder metal assemblies is in their method of thread creation.
The process of Self-Tapping will often result in the creation of chips, or swarf when referring to metal, a byproduct of cutting the material during installation.
Whilst this is not a complication for all assemblies, for harder materials and sensitive applications this can result in contamination and use of Thread Rolling Screws can minimise this risk.
As the material around the thread is compressed rather than cut as the Thread Rolling Screw is installed, these fasteners are also more resistant to vibration and loosening in comparison to standard Self-Tapping Screws.
So should you choose a Thread Rolling or Self-Tapping screw? Ultimately, if your project involves higher grades of aluminium or similar materials, is higher-stress and requires stronger and more secure fasteners, Thread Forming Screws would be the best choice.
Alternatively, if ease of installation and versatility are a higher priority and your project involves softer materials, Self-Tapping Screws would be suitable.
Where Would You Use A Thread Rolling Screw?
Though Thread Rolling Screws are most commonly used in metal assemblies, they can be used in other hard materials such as some types of plastic.
Can Thread Rolling Screws Be Used In Metal?
Within the manufacturing industry, Thread Rolling Screws are often used in metal applications.
As a removable and reusable fastener that can be installed without a pre-tap hole, these screws are commonly used in aluminum extrusion to create fixings in molded holes to save time in manufacturing.
Components that are used in manufacturing will typically be exposed to constant movement, where standard machine screws can begin to loosen over time.
This can become a hazard if the component loosens too much, and can also take up valuable running time for them to be re-tightened.
Thread Rolling Screws are designed to perform well in these dynamic environments, providing further resistance to pull-out vibration, whilst also not requiring nuts or inserts for installation.
Thread Rolling Screws are also often used in metal assemblies as an alternative to Self-Tapping Screws. In many instances, they are the preferred component as they do not produce swarf when they are installed.
In some instances, Thread Rolling Screws can be used as an alternative to interlocking male and female components to avoid the complications ensued by cross-threading.
Cross threading is the term used to describe the misalignment of a male and female thread. When the two threads are not aligned, they can become jammed or fractured. This often occurs when the holes are not perpendicular or when there is damage to the thread during the tapping process.
As they form their own threads in an assembly, Thread Rolling Screws are not being inserted into an existing thread, subsequently removing any risk of cross-threading.
To find out more about Cross Threading and how to avoid it head to our technical article, ‘How To Avoid Cross Threading’.
Can Thread Rolling Screws Be Used In Plastic?
For similar reasons that they are used in metal, there are many benefits to using Thread Rolling Screws within plastic assemblies.
Just like metal, there are types of plastic that are too hard and dense for standard Self-Tapping or machine screws.
Without the appropriate preparation, such as the use of a pilot hole, if you were to try and fasten one of these standard screws into a plastic assembly, it is likely that you would encounter significant resistance and stripping.
Though Self-Tapping Screws are designed to tap their own threads, they are unsuitable for harder plastics, just as they are unsuitable for harder metals.
Thread Rolling Screws, by comparison, are specifically designed for these material types.
For example, they have a trilobular shape that enables them to create threads in plastic with minimal driving torque. Additionally, these screws exert less outward pressure by forming the material, which decreases the likelihood of a screw boss bursting.
Nevertheless, these components are not quite as effective for plastic assemblies as other, more specialized, fasteners such as Polyfix or Plastite Screws.
These screws use the same method as Thread Rolling Screws to form a thread but have added features to make them more effective for use in plastics.
Polyfix and Plastite Screws are a type of fastener that have a specialised sharp thread profile and trilobular shape making them ideal for plastic installations. The sharper thread profile allows the fastener to cut deeper into an assembly whilst also reducing the likelihood of stripping. This trilobular shape also reduces friction during the thread-forming process.
Learn more about Polyfix Screws by heading to our technical article, ‘Polyfix Screws: Self-Tapping Screws For Plastic’.
Custom Manufactured Thread Forming Screws
Does your project have specific requirements for Thread Rolling Screws that you can’t seem to find on our website? Accu can manufacture these to your specifications, with a range of custom lengths and head types available.