3 min read


Extension Spring

When the average person thinks of springs, they most likely envision an extension spring. Extension springs stretch and get longer, then return to shape. Slinkies are extension springs. So too are screen door mechanisms.

But extension springs are much more than toys or door closers. When used in industry or manufacturing, extension springs come in all shapes and sizes and serve all kinds of purposes.

In this article, we provide an overview of extension springs, their styles, their common uses, and why Spring Dynamics should be your extension spring maker of choice.

Custom and Prototype Spring Manufacturer

What Are Extension Springs?

Extension springs supply a pulling force. These springs are made from various grades and alloys of round spring steel material. There are various hook configurations that can be applied to extension springs including; Machine hooks, German hooks (arbor cut or extended tabs), English or cross center hooks (as shown below), and side or edge hooks.

Extension springs store energy and exert a pulling force between two mechanisms. When mechanisms separate, the extension spring tries to bring them together again. Extension springs use round wire to create a close-wound design with initial tension.

An extension spring’s ends attach between two mechanisms. The extension springs hooks and loops store and absorbs energy. Through hooks or loops, an extension spring provides return force to connected mechanisms.

More stress in the end hooks—as opposed to the spring body—limits the performance of extension springs.

Styles of Extension Springs

The most commonly used end styles for extension springs include German-style, machine hook, cross-center, side hook, and double loop ends.

German-style and machine-style ends are the most common end styles. On a German-style hook, the hook radius is extended further from the coil body than the distance of the coil body’s inner radius.  The machine-style end has a hook that is raised from half of the coil body so that the inner radius of the hook is equal to the inner radius of the coil body, and the hook radius is as near to the coil body as possible.  Both function in the same way mechanically.  German-style hooks are slower to produce but yield more consistent hook geometry.  Machine hooks are produced in a simpler fashion, therefore have a shorter cycle time, but the trade-off is less consistent hook geometry.

Manufacturing Industries and Products That Use Extension Springs

  • Garage doors: Garage doors may be one of the most well-known extension spring applications. These are the springs that attach to the sides of your door that come into play when you attempt to raise or lower the door, helping to mitigate some of the strength needed to lift or close a door that may weigh hundreds of pounds. Take note of the distinction between torsion springs, another common type of garage door spring that works from above the door, and extension springs, which work from the sides.
  • Automotive: You may not find extension springs as much in modern cars, as they were a key component of your vehicle’s carburetor. However, there are still a number of automotive extension spring uses both on the inside and the exterior of your car.
  • Trampolines: Trampolines are another very popular use of extension springs. You can see them in action as you or your family members jump up and down since extension springs enable the trampoline to bounce. In fact, every trampoline may have hundreds of extension springs.
  • Toys: In the past, many more toys utilized extension springs for shooting actions, but both the tiny springs themselves and the projectiles they fired were considered unsafe for children. You will still find extension springs in many toys, particularly toys that have fast motion or throwing actions, especially toys for older kids. Some very safe and popular toys that use extension springs include windup toys and pinball machines.
  • Pliers: The vise-grip type of pliers that not only grip but can be locked into position to keep the grip tight use extension springs, which are employed to hold the grip in place.
  • Washing machines: A washing machine is probably one of the last things you might think of when it comes to mechanical extension spring applications, but in fact, they are a critical part of the machinery. When you activate your washing machine, the drum spin at high speed to agitate the clothes and enact the washing process. Without extension springs to hold the drum in place, that spinning drum would bang against the sides of the machine, bouncing it all over the room and making a lot of noise as you do your laundry.
  • Medical devices: For centuries, the medical world has relied on springs to function. You can be sure that includes extension springs. You can find extension springs in stretchers, surgical lights, and more.
  • Farm equipment: Just as many automobiles use extension springs, farm vehicles use them, as well. However, they are especially useful for farm vehicles because these machines are so heavy and require so much pulling strength. You’ll find them in combine harvesters, tractors, and more, in applications ranging from transporting goods to plowing fields and everything in between.
  • Baby carriages: If you appreciate the gentle bouncing that rocks your child to sleep as you wheel them around town, you just might have a suspension facilitated by extension springs to thank.
  • Fence gates: Enjoy the way your front gate bounces back and snaps shut after you go through it without you having to do anything? That’s extension springs at work.
  • Choose Spring Dynamics for Your Extension Springs

Spring Dynamics manufactures extension springs for a variety of industries and applications. Each spring design is engineered to function in whatever assembly our customer needs. In order to ensure the whole assembly works in harmony, Spring Dynamics works to understand the end-use for each spring and incorporate that knowledge into the customer’s design.

Your product development team is welcome to work with our engineering group to identify which extension spring will work best for your application – in many cases providing advantages not previously considered.

Custom and Prototype Spring Manufacturer

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Extension Spring


When the average person thinks of springs, they most likely envision an extension spring. Extension springs stretch and get longer, then return to...

Read More