Rapid Custom Extension Spring Manufacturing
Extension springs, also called tension springs, are some of the most versatile spring types in mechanical design. We manufacture custom extension springs in low volumes with fast turnaround, supporting R&D programs, prototype builds, replacement parts, and short-run production across a wide range of industries.
Our engineers work directly with you from the first sketch through delivery, including design assistance, material selection, and guidance on end configuration. There's no minimum order quantity.
What Is an Extension Spring?
An extension spring is a closely-wound helical spring designed to resist tensile force. Unlike a compression spring, which pushes back when you squeeze it, an extension spring pulls back when you stretch it. It stores energy as it extends and releases that energy to pull components back to their original position.
Extension springs are wound with initial tension, a preload built into the spring during manufacturing that determines how much force it takes to begin opening the coils. The end configurations, meaning the hooks or loops at each end, are critical design elements. They determine how the spring attaches to mating components and where stress concentrations build up.
End Configurations for Custom Extension Springs
The end configuration is one of the most important decisions you'll make for an extension spring. We manufacture the following end types:
• Full loops (machine loops), the most cost-effective standard end configuration
• Half loops, used where you need a reduced loop height
• Crossover loops, which add strength at the hook-to-body transition
• Extended hooks, for applications where the hook needs to reach beyond the spring body diameter
• Side hooks and other special configurations, for unique attachment needs
One thing worth knowing: the hook-to-body transition is the highest-stress spot on an extension spring. Getting the bend radius right at that junction makes a real difference in fatigue life, and it's something our engineers pay close attention to during design review.
Applications
• Industrial machinery, including counterbalance mechanisms, door closures, and tensioning systems
• Automotive, including hood latches, seat mechanisms, and throttle return springs
• Medical devices, including surgical instruments, diagnostic equipment, and medical device components
• Consumer products, including appliances, toys, and sporting goods
• Aerospace, including control surface mechanisms and retention systems
• Electronics, including contacts, latching mechanisms, and keypad return springs
Extension Spring Design Parameters
To spec out a custom extension spring, here's what we'll need:
• Wire diameter
• Outside diameter
• Free length (the relaxed, unloaded length)
• Initial tension, the preload force built into the spring
• Spring rate, the force per unit of extension (lb/in or N/mm)
• Number of active coils
• End configuration: type, orientation, and position of hooks or loops
• Material, plus any finish or plating requirements
Frequently Asked Questions: Custom Extension Springs
Q: What is an extension spring and how does it differ from a compression spring?
A: An extension spring, also called a tension spring, is a closely-wound coil spring that resists stretching. It pulls back when extended. A compression spring resists being compressed and pushes back when squeezed. Extension springs have closed coils with built-in initial tension and hook or loop ends, while compression springs have open coils with flat or ground ends.
Q: What end configurations are available for extension springs?
A: We manufacture extension springs with full loops (machine loops), half loops, crossover loops, extended hooks, side hooks, and custom end configurations. The right end type depends on how the spring attaches to mating components and the stress requirements of the application.
Q: What causes extension springs to fail, and how can it be prevented?
A: The most common failure point is the hook-to-body transition, where stress concentration is highest. The main ways to extend fatigue life are getting the bend radius right at that transition, specifying the correct initial tension, and keeping stress levels below the material's elastic limit. Our engineers review all of this during design and quoting.
Q: What is initial tension in an extension spring?
A: Initial tension is a preload built into an extension spring during winding. The coils are wound tightly enough that a minimum force is needed before the spring starts to extend. It keeps the coils closed under light loads and is specified as a force value, in pounds or Newtons.
Q: What is the minimum order quantity for custom extension springs at Quick Spring?
A: There isn't one. We manufacture custom extension springs from a single piece up to large volumes.
Extension Spring Material Options
Request a Custom Extension Spring Quote
Quick Spring Capabilities