What is Extension Spring?- Working, and Application

What is an Extension Springs?

Extension springs absorb and store energy as well as create a resistance to a pulling force. These springs are usually attached to other components at both ends and when those components come apart the spring tries to bring them back together again.

It is the initial tension that determines how tightly together the spring is coiled. This initial tension can be manipulated to meet the load requirements of a particular application. Designs usually have hooks, eyes, or other interface geometry on the ends that attach to the opposing components.

They are often used to provide a restoring force to components that extend in an actuated position.

How do Extension Springs work?

Extension springs generally have a hook or eye at each end to facilitate attachment. Variations on the ends include open hooks, extended hooks, side hooks, and double full loops.

Extension springs are often used to create a restoring force in mechanisms such as latches and counterbalances. Since extension springs are under tension, they do not need any support along their length. This often results in a simpler mechanism than if a compression spring were used.

The ends of an extension spring are attached between two mechanisms. The hooks and loops of the tension spring store and absorb energy. An extension spring provides the connected mechanisms with a restoring force through hooks or loops.

Tightly coiled extension springs typically sit in the idle position. More stress in the end hook in contrast to the spring body limits the performance of extension springs.

Extension springs

Key Design Parameters


  • Outside Diameter, Inside Diameter, Wire Diameter, Free Length and Extended Length
  • The Free Length is the length of a spring in the unloaded position (measured from inside the end loops).
  • The Extended Length is the length at full rated extension.

Spring Rate and Maximum Load

  • The Spring Rate is the force per unit spring deflection, such as lbs per inch travel.
  • The Maximum Load is the load at full rated extension.
  • Unit of Measure


Extension springs use a variety of hook or loop end configurations to serve specific functions. Tension spring ends include threaded inserts, extended twist loops, crossed center loops, hooks, expanded eyelets, reduced eyelets, square ends, and teardrop-shaped ends.

Change the length of the hooks and spring body spacing for custom tension spring fits and functions.

Find extension springs in a wide variety of everyday items from garage doors to tools to washing machines and toys. The variety of sizes makes extension springs versatile as they are used in small medical devices and off-road machines.

Common applications of extension springs include:

  • Car interiors and exteriors
  • Garage door assemblies
  • Vise-grip pliers
  • Carburetors
  • Trampolines
  • Washing devices
  • Farm machinery
  • Toys


What is spring rate extension spring?

The change in load per unit of deflection, generally expressed in pounds force per inch. Spring rate is determined by the amount of force, in pounds, required to extend a spring by one inch. Material size directly impacts spring rate.

Which is better torsion or extension springs?

Torsion springs tend to be stronger and more durable than extension springs. And though they are more expensive, they last longer, between 15,000 and 20,000 cycles as opposed to 10,000 cycles with extension springs. They also offer greater balance and show more control when moving, not jerking as the door moves.

What is the difference between compression and extension springs?

Compression springs differ from extension springs in regards to how they work. While extension springs become longer under a load, compression springs become shorter. Compression springs are designed for use in applications where two components try to push towards each other.

How do extension springs work?

Extension springs absorb and store energy as well as create a resistance to a pulling force. These springs are normally attached at both ends to other components and when these components move apart, the spring tries to bring them back together again.

Do you need extension springs with a garage door opener?

This means that you shouldn’t use your garage door opener without any springs since residential openers don’t typically have much horsepower. So, your opener doesn’t actually do much lifting – garage door springs are used to lift the weight and provide balance.

How long do extension springs last?

Extension Springs’ Life Expectancy: Extension springs are installed at the side of the door and act extend, rather than contract (as does the torsion spring). They have 15,000 and 20,000 cycles which equate 7 – 12 years of life expectancy.

Are torsion springs safer than Extension springs?

Torsion springs are safer than extension springs and often last twice as long. Coating a torsion spring makes it last even longer than a regular torsion spring.

What is the formula for extension?

Hooke’s Law states that the force needed to compress or extend a spring is directly proportional to the distance you stretch it. As an equation, Hooke’s Law can be represented as F = kx, where F is the force we apply, k is the spring constant, and x is the extension of the material (typically in meters).

What is extension and compression?

Extension Spring. A compression spring is meant for shortening its length under the action of external force. An extension spring is meant for increasing its length under the action of external force. The compression spring will push the structural member to increase its length.

What is an extension spring made of?

Most extension springs are coiled springs manufactured from sprung steel spring wire. Generally, extension springs have a hook or an eye at each end to facilitate fastening. Variations on the ends include open hooks, extended hooks, side hooks, and double full loops.

How do extension springs store energy?

Extension springs extend as you apply force to them, pulling apart the coils. Their resistance against this force stores mechanical energy within the coil. When you remove the force, the spring releases its mechanical energy by snapping back into its original state with no pitch between coils.

How do I choose a spring extension?

The weight that shows on the bathroom scale is the size extension spring you need to order. For a two-car garage door, carefully lower the garage door onto two-bathroom scales. Each scale should be located approximately two feet from each side.

What is the difference between torsion and extension garage door springs?

Extension springs fully expand and contract when operating an overhead door. Torsion springs turn. Torsion springs are sturdier and last longer. Torsion springs do cost more but generally last between 15,000 and 20,000 cycles, whereas extension springs last up to 10,000 cycles.