What is torque and why does it matter for hardware installation?
Even if you don't hear the term often, torque is a force at work in countless everyday actions. It powers our cars, opens our doors, and—most importantly here—twists our screws. When it comes to fastening, understanding torque isn't just about technical knowledge; it's what separates a secure, reliable connection from one that fails too soon or damages materials.
This article provides a clear, practical foundation for understanding torque and its role in screw installation. Having this knowledge, as well as proper technique, will allow you to get consistent and accurate results with every fastener you install.
Understanding torque
In this section, we'll define torque in a technical context. Afterwards, we will explore how it applies to fasteners.
Technical definition of torque
Torque formula
𝜏 = r * F
- 𝜏 is torque
- r is the distance from pivot point to point of force
- F is applied force
This is a simplified explanation of torque, but the concept can easily become complex. Here are some key points you should understand:
- Torque is turning power.
- Torque increases as applied force (F) increases.
- Torque increases as tool length (r) increases.
Torque in screw installation
Torque plays an active role in the screw installation process. As you insert a screw, you are applying torque that twists the screw into the material, generating the clamping force that holds the joint together.
Tool length contributes to the amount of torque applied to a fastener. With bolts, the relationship between tool length and torque is straightforward. The length of the wrench acts as r, which is why a longer wrench allows you to generate more torque with the same applied force.
Unlike bolts, screws are driven along the axis of insertion, so there is no perpendicular lever arm like a wrench. Instead, the radius r relates to the radius of the screwdriver handle where force is applied. This shorter radius means it requires more applied force to generate the same amount of torque.
Resistive torque
All fasteners face resistive forces, such as friction, that make them harder to install. Friction between the fastener and the surrounding material contributes to resistive torque, which is the force that must be overcome to drive the screw.
The total, or net, torque is equal to the applied torque (from the screwdriver) minus the resistive torque (from the surrounding material).
𝜏net = 𝜏applied - 𝜏resistive
Have you noticed that twisting a screw becomes more difficult the deeper it is driven into the material? This is because resistive torque from friction increases as the screw is driven.
With each twist of the driver, more surface area touches the material, creating more resistive torque. Friction peaks when the screw bottoms out—this is when a driver begins to strain, and you should stop to avoid overtightening.
This leads to an important principle in fastener installation: tightening to a specific torque.
Tighten to a specific torque
When instructed to tighten a fastener to a specific torque (let's call this x), you should tighten until the applied torque reaches x. Torque specifications refer to the applied torque from the tool, not the net torque after considering resistance.
When applied torque equals x, the screw should be snug in the material. Driving to a higher torque risks overdriving, splitting material, or stripping the screw. Failing to meet the required torque may result in a loose screw or unstable joint.
Tools such as torque screwdrivers measure applied torque during installation, making it easier to tighten fasteners correctly. In the next section, we'll cover how torque requirements vary across different screw types.
Torque and screw design
Each screw has a unique recommended torque rating, which is the amount of applied torque needed to properly secure the fastener. This rating is influenced by various factors, including:
- Screw length and width—the fastener size affects how much surface friction must be overcome.
- Screw material—softer metals are more likely to deform or strip under high torque, while harder metals resist deformation.
- Drive type—certain bit designs are better suited for high levels of torque.
The chart below shows general trends in torque capacity by fastener material, drive type, and size. Keep in mind that torque capacity depends on many factors, and you should always check with the manufacturer if you need exact specifications.
Although it may be tempting to try to maximize torque by choosing the largest or strongest screws available, it is sometimes better to use smaller or softer screws if they meet the structural requirements of your project.
For example, Phillips head screws are intentionally designed to cam out under high levels of torque to reduce the risk of overtightening. So before dismissing them as "weaker," consider adjusting your technique if you repeatedly strip Phillips head screws.
For highly specified projects, it is best to get the manufacturer's recommended torque specifications for your fasteners. But for most minor projects and repairs, a reliable rule of thumb is to stop tightening when the screw is snug. Overdriving can damage both the fastener and the surrounding material.
Summary
By building a solid understanding of torque and how it applies to fastening, you can improve both the consistency and reliability of your installations. Here are some key points to take away from this article:
- Torque is the twisting force applied to a fastener.
- Torque increases as applied force and tool length increase.
- Screws made of harder metals can generally handle more torque, while softer metals are more likely to deform or strip.
- The torque required to drive a screw increases as it is inserted farther due to friction.
- Always tighten screws to their specified torque rating to avoid overdriving or loose joints.
If you have any questions about fasteners or need help planning your next job, please don't hesitate to contact our friendly experts by calling (406)752-5253 or by sending an email to tom@jakesales.com.
FAQ
Why is proper torque important in screw installation?
Applying the correct amount of torque ensures the fastener is tight enough to hold your material securely without causing damage. Under-tightening can create loose joints, and over-tightening can damage the screw or surrounding material.
What happens if I use too much torque when driving my screws?
Using too much torque can lead to over-tightening the fastener. This can reduce holding strength by stripping the threads, snapping the screw, or damaging the surrounding material. In some cases, it can make future removal difficult or impossible.
What happens if I use too little torque when driving my screws?
Using too little torque can lead to under-tightening the fastener. This can create an unstable or loose joint, especially for load-bearing projects or projects exposed to vibration.
How can I find the correct torque for a screw?
Many factors such as screw size, material, and thread type affect the correct amount of torque for a fastener. For accurate values, it's best to check the manufacturer specifications.
Does screw material affect torque?
Yes—harder materials like stainless steel or hardened steel typically have a higher torque capacity, while softer materials like aluminum or brass require lower torque to avoid damage.
What tools are best for applying precise torque?
Torque screwdrivers and torque wrenches are designed to apply a specific, repeatable amount of torque. These tools are ideal for applications where consistency and accuracy are important.
How can I prevent over-tightening my screws if I don't have a torque driver?
Most drills have adjustable clutch settings that help limit torque, but they are not highly precise. For critical applications, a torque screwdriver or torque wrench is recommended. But for many at-home projects, tightening fasteners until they are snug—not more and not less—provides a secure connection.