6 Facts About Extension Springs | OneMonroe - Monroe Engineering

Extension springs are commonly used in furniture, household appliances, garage doors and countless other everyday products. Also known as tension springs, they are designed to operate under a tension load. Here are six facts about extension springs.

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#1) Create a Pulling Force

While other types of springs may create a pulling force, extension springs create a pulling force. When exposed to a tension load, they will store mechanical energy while simultaneously creating a pulling force. Therefore, you can use an extension spring to hold two components together. As it creates a pulling force, it will prevent the components from separating.

#2) Typically Features Hooks on the Ends

You can find extension springs in different styles, but most of them have hooks on the ends. There’s a single hook at each end. What’s the purpose of these hooks exactly? They allow the extension springs to connect to components. You can slide the hooked ends of an extension spring over the components.

#3) Opposite of Compression Springs

Extension springs are essentially the opposite of compression springs. There are over a dozen types of springs, but most of them fall under one of two categories: extension or compression. Extension springs are designed to operate under a tension load, meaning they become longer while creating a pulling force. Compression springs, in comparison, are designed to under a compression load, meaning they become shorter while creating a pushing force.

#4) Made of a Single Piece of Metal

Most extension springs are made of a single piece of metal. The metal stock is placed into a machine known as a former. The former will then bend the metal to manipulate it into a coiled shape. Some extension springs are made of stainless steel, whereas others are made of carbon steel or music wire steel. Regardless, most extension springs consist of a single piece of metal in a coil shape.

#5) Designed to Stretch Up to a Specific Length

Extension springs are designed to stretch up to a specific length. This maximum stretch length is known as an extension limit. While under a tension load, an extension spring will begin to stretch while becoming longer. It will only stretch up to the spring’s extension limit, however.

#6) Stretch Is Determined By Several Factors

Several factors affect the strength of an extension spring. Some of these factors include the material, thickness and length. Generally speaking, the longer and thicker an extension spring is, the stronger it will be.

A stock extension spring is a premade in-stock off the shelf mechanical spiral spring device designed to store and release energy through a pulling force. Unlike compression springs, which resist compressive force as they are compressed, extension springs are made to resist force when pulled apart. Typically made of round spring wire, these springs are helically wound, with the coils touching one another in their free, unstretched state. This compact stock extension spring configuration enables the spring to store a significant amount of energy called initial tension that's used when stretched. When the tension is released, the spring returns back to its original length, making extension springs ideal for applications that require controlled pulling forces or where energy must be absorbed and released.

Stock extension springs are commonly used in applications where tension is necessary to maintain a certain distance between two components. They’re found in everything from lightweight household products, like screen doors, to heavy-duty machinery in industries like construction and aerospace. Their ability to store and release energy consistently over repeated cycles makes them indispensable in many mechanical designs. At Acxess Spring, we believe that understanding the nuances of extension springs—from their physical properties to their specific applications—empowers innovators and manufacturers to create more reliable, efficient, and effective products.

The spring rate (k), or spring constant, of an extension spring is a measure of how much force is required to extend the spring by a given distance. Understanding this value is critical when designing or selecting a spring for a particular application, as it helps determine how the spring will behave under load.

The formula for calculating the spring rate is:

 k = Gd^4 ÷ (8D^3 * n)

Where:

• G is the modulus of rigidity of the spring material (a measure of the material’s stiffness),
• d is the wire diameter,
• D is the mean coil diameter (the average of the inner and outer diameters),
• N is the number of active coils.

For example, on Axcess Spring’s Part number PE045-500--MW--CO-N-IN where wire diameter is 0.045 inches, the mean diameter is 0.455 inches, has a material shear modulus (G) of .929 ps and counts with 36.33 total coils, the formula would be solve like this:

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The load that an extension spring can handle is an essential factor in determining its performance within an application. To calculate the load, you begin by multiplying the spring’s Rate (R) by the Distance Traveled (DT), which is the amount you expect the spring to extend under a given force. The formula for this calculation is straightforward:

Rate × Distance Traveled = Load

Or more specifically:

R × DT = L

If we need to calculate the load for Axcess Spring’s Part number PE045-500--MW--CO-N-IN traveling to a distance of 2.5 inches with a spring rate of 1. lbs/in, we’ll do the following calculation:

R × DT = L

1. x 2.5 = 4.

This means that if you know how much the spring will stretch and the spring’s rate (which is a measure of its stiffness), you can calculate the load it will experience, in this case 4. lbf. However, this is only part of the equation. Most extension springs have an initial tension—a pre-loaded tension that needs to be overcome before the spring begins to extend, for Part number PE045-500--MW--CO-N-IN the initial tension is 0.913 lbf. Therefore, once you have the calculated load from the above formula, you must add the initial tension to get the true load at a specific distance traveled. This gives you a more accurate idea of the total force the spring will experience during operation, helping to ensure that it will meet the performance and safety requirements of your application. Now let’s calculate the load adding the initial tension: 

L + IT

4. + 0.913 = 5.216 lbf

At Acxess Spring, we are dedicated to providing high-quality, custom, and stock extension springs for all types of applications. Whether you're developing a cutting-edge medical device, designing industrial machinery, or creating innovative consumer products, our extensive catalog and the powerful tools we offer, like Spring Creator 5.0, ensure that you’ll find the perfect spring for your needs.

We offer a wide selection of extension springs in various materials, sizes, and end types, as well as the option to fully customize your springs to meet the unique demands of your project. By partnering with Acxess Spring, you gain access to decades of expertise, top-tier manufacturing standards, and the innovative tools you need to bring your vision to life.

Empower your projects with precision-engineered springs that deliver reliability, performance, and durability—every time.

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