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Products > Springs

Extension Springs

Helical Extension springs or Tension springs store energy and exert a pulling force. Usually, they are manufactured with round wire and close-wound with initial tension. All industries including aerospace, medical, industrial automation, and automotive use extension springs. Extension springs are used in balance scales, garage doors, toys, furniture, trampolines, automatic washing machines, and thousands of other applications. Extension springs unlike compression springs do not have a solid stop to prevent overloading, so it is critical to know how far it is safe to extend the spring. The initial tension in extension springs is a critical parameter which is defined as the initial force needed to separate adjacent coils.

Century Spring offers a large variety of stock Extension springs and can manufacture custom extension springs for any application and industry. For available stock options please explore our user-friendly search engine or contact us for assistance, you can also request a quote for your custom spring inquiries.

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Extension Springs Overview

How Extension Springs Work

Extension springs are designed to absorb and store energy as well as create a resistance to a pulling force. The “initial tension” is created during manufacturing when the wire is rotated backwards during coiling. It is initial tension that determines how tightly together an extension spring is coiled. When you pull the spring apart, you are undoing the rotation, which develops force or initial tension. Initial tension can be manipulated to achieve the load requirements of your particular application.

Century Spring's Extension Springs

Century Spring's extension springs are wound with an initial tension force which offers a small deflection load for secure installation “holding”. The initial tension is equal to the minimum force required to separate adjacent coils. Each spring is of the constant diameter type with a variety of hook/loop styles. Tolerances for extension spring rates depend upon the body diameter to wire diameter but are usually +/- 10% and +/- 5% on the diameter. The initial tension is much more difficult to control and is offered as a reference value only.

Not sure what extension spring you need? Review our Selection Guide for Extension Springs.

Spring Anchors are also available.

Custom Extension Springs

Century Spring specializes in custom fabrication of extension springs and has vast manufacturing capabilities beyond our competitors; whether you require a spring with extreme length, heightened performance, or quality certified products, we have you covered.

Our solutions approach is not limited to manufacturing. We specialize in prototyping, design, and tooling. We will work with your team and preferred specifications to assist you in developing the best spring for your application.

Ready to get started? Request a Quote.

Extension Spring Manufacturing

If you are looking for industry-leading expertise for extension springs, you’ve come to the right place. Our teams are comprised of experienced manufacturing technicians and engineering experts who are committed to developing the right products to suit your needs. Our experts can produce extension springs of various thicknesses and lengths using both cold and hot coiling processes.

Another advantage of working with Century Spring is that we maintain stock of numerous alloys. The advantage is that if a couple of prototypes are needed, our in-house stock gives us the ability to develop them in a cost-effective way.


We also offer a variety of treatment and finishing options for custom springs made from standard or specialty materials. Certifications of conformance for geometric tolerances for stock springs are available upon request. Material certifications are available for custom springs.


  • Beryllium Copper
  • Bronze
  • Hastelloy®
  • Inconel®
  • Monel
  • NiSPAN-C®
  • Stainless Steels
  • Steel (including: Chrome Silicon & Chrome Vanadium)
  • Tantalum
  • Titanium (Beta-C)


Our extension springs can be manufactured with a selection of commonly requested or specialty finishes.


  • Black Oxide
  • Color Coding
  • Gold Irridite
  • Nickel
  • Passivation
  • Plating
  • Powder Coating
  • Silver
  • Tin
  • Zinc

Wire Types

We produce extension springs from both bar and wire stock in a variety of thicknesses through both hot and cold coiling methods. More details are listed below:


  • Wire and Bar Stock: 0.008" - 0.750"

Direction of Helix (Wind)

We can configure your extension springs in either a left or right wind configuration to suit your specific application.


  • Left
  • Right


The ends on the extension springs offered in our stock inventory are the common machine-made hook and full-loop configurations. The hooks or loops may have an across center transition of the last coil before forming the hook or loop. The angle between hook/loop planes (end position) is random. If you need a specific end configuration, contact us for design support and quoting.


To accurately measure an extension spring, follow the steps below.

  1. Hold the spring in one hand, and the calipers in the other hand.
  2. Place the calipers across the outside coil, either at the end or the center of the spring. This is called the Outside Diameter (O.D.).
  3. Place the calipers on the wire at one end of the body coil of the spring. This is called the Wire or Material Size.
  4. Place the calipers (or tape measure) on the full length of the spring, inside the hooks. This is called the Length (L.I.H.). (see diagram for example)

Browse Other Coiled Spring Products

  • Compression Springs
  • Torsion Springs
  • Die Springs
  • Hot Wound Springs
  • Cold Wound Springs
  • Antenna Springs & Assemblies
  • Garter Springs
  • Tapered / Barrel Springs

Need a Large Order?

We can design and manufacture a component for your specific application in any quantity. For quantities over 1,000, please request a quote.

Request a Quote

Century Spring Catalog

Century Spring Catalog

From compression springs and extension springs to retaining rings, the Century Spring catalog contains details on thousands of parts available for same-day shipping. Download the catalog now or contact us to request a physical copy.

View PDF Catalog