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316 Stainless Steel

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Long Length - Stainless Steel

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Long Length - Carbon Steel

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Stock extension springs in carbon steel and stainless steel

Extension Spring Overview

India Spring Parts warehouses the largest inventory of high-grade extension springs in the world. Extension springs are designed to absorb and store energy as well as create a resistance to a pulling force. It is initial tension that determines how tightly together an extension spring is coiled. This initial tension can be manipulated to achieve the load requirements of your particular application. All India Spring Partsextension 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. Spring Anchors are also available.

Extension Spring Details


  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)


The highest grades of spring wire are used in manufacturing India Spring Parts products. Certifications of conformance for geometric tolerances for our stock springs are available upon request. We only offer material certifications for custom springs.

“Spring steel” is a term that includes music wire, hard-drawn wire and oil-tempered wire. Alloy steels for stock extension springs are offered only in 300 series stainless.


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.


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, it is best to contact our custom spring department.

Extension spring end styles from India Spring Parts.


Our stock extension springs contain a selection of commonly requested finishes:

  • Zinc
  • Gold Irridite
  • Black Oxide
  • Passivated (upon request)
  • None (can be plated upon request)

Custom manufacturing from prototype to full production