What Are Extension Springs?

Extension springs are a type of industrial spring designed to store and release energy when subjected to a pulling or tensile force. These springs create tension and provide a return force when the spring is stretched or extended. Extension springs typically consist of a helical (coil) design, where the wire is wound into a spiral shape.

Apex’s extension springs are made from a variety of materials, including chrome silicon, music wire, pre-coated material, and stainless steel. They are offered in wire sizes ranging from .018” to .156” in diameter.

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End Types

NOTE: These types can be changed to fit the specific types Apex manufactures. We can also include pictures of the different types here if requested, using Apex’s own product pictures if available.

Extension springs have various end types or configurations to suit different mounting requirements. The choice of extension spring end type and design depends on load capacity, extension length, operating temperature, and environmental conditions. These end types play a crucial role in how the spring interacts with the objects it’s connected to.

Here are some popular types of extension spring end types and the various industries where they are commonly used:

Machine Hooks

Machine hooks are the most basic extension spring end type. They consist of simple, tightly wound coils at each end of the spring. These hooks are ideal when the spring will be attached with the help of external components, such as pins or fasteners.

  • Automotive Industry
    Machine hook extension springs are used in the automotive industry for components like seat recliners, trunk and hood latches, and door handles.
  • Manufacturing and Machinery
    They find use in conveyor systems, garage doors, and machinery where controlled extension and retraction are required.

Cross-Center Hooks

Cross-center hooks, also known as cross-over center hooks, have one hook that crosses over the center of the spring to connect with the coils on the opposite side. This design helps to equalize the stress on both ends of the spring and provides stability during operation. Cross-center hooks are often used when the spring needs to be suspended and extended in a straight line.

  • Aerospace Industry:
    Cross-center hook extension springs may be used in retractable landing gear and cabin components, where precision and strength are crucial.
  • Medical Devices:
    These springs can be found in medical devices and equipment that require controlled linear motion or tension, like surgical instruments and hospital beds.

Double Full Loop Hooks

Double full loop hooks feature two complete loops or hooks at each end of the spring. These hooks provide a secure and stable attachment point for various uses. They are commonly used when the spring needs to be secured with bolts, pins, or other hardware.

  • Industrial Manufacturing:
    Double full loop hook extension springs are commonly used in industrial equipment, such as manufacturing machinery and assembly line systems.
  • Agriculture
    Used in farming equipment for functions like tensioning belts and cables on agricultural machinery.

Side Hooks

Side hooks are designed with one or more hooks located on the sides of the spring rather than at the ends. This configuration allows for broader attachment options, making side hooks versatile. They are commonly used when space constraints or specific mounting requirements make traditional end hooks less suitable.

  • Construction Industry
    Side hook extension springs can be used in construction equipment, such as cranes, to assist with various lifting and tensioning functions.
  • Renewable Energy
    Wind turbines often use side hook extension springs for maintaining tension in cables and components.

Extended Hooks

Extended hooks have longer hooks or arms, which can facilitate easier attachment and provide additional flexibility in mounting the spring. These hooks are useful when you need extra reach for attaching the spring to your application. Extended hooks are often used when the attachment points are far from the spring’s coil body.

  • Marine Industry
    Extended hook extension springs are used in the marine sector for securing hatches, doors, and other equipment on ships and boats.
  • Oil and Gas
    Extended hook extension springs are used in the marine sector for securing hatches, doors, and other equipment on ships and boats.

Apex can help design and manufacture the right spring for your project? Contact us, call 616.453.5463 or request a quote today!

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Advantages of Using Extension Springs

Extension springs have several advantages due to their unique design and characteristics. These advantages include:

Elasticity and Energy Storage

Extension springs are designed to store and release energy when stretched. When you pull on an extension spring, it resists the force applied and stores potential energy. This stored energy can be released to perform work when the force is reduced or removed. This characteristic makes extension springs ideal for situations where controlled force or motion is required.

Linear Force Output

Extension springs provide a relatively constant force over their range of motion. This makes them valuable where a consistent and predictable force is necessary, such as in automotive suspensions, garage doors, and industrial machinery.


Extension springs can be customized for specific force, length, and size requirements. Manufacturers can design extension springs with various configurations, such as different end types (e.g., hooks, loops, or eyes), to suit different mounting and attachment methods.


Extension springs are typically made of durable materials, such as high-quality steel alloys, that can withstand repeated cycles of stretching and contracting without experiencing significant fatigue or failure. This durability is crucial in situations where the spring will undergo many cycles.


Extension springs can be designed with safety features, such as double loops or other end configurations, to prevent them from dislodging or inadvertently releasing their energy.


Extension springs are generally cost-effective and can provide a cost-efficient solution for situations where controlled force or tension is required.

Why You Should Choose Apex Spring & Stamping

Located in Grand Rapids, Michigan, Apex Spring & Stamping provides world-class manufacturing anywhere in the USA. Apex has served customers in the recreational, automotive, office furniture, medical, appliance, and consumer markets since 1977.

Whether you require small springs and clips or large stampings, wireforms, slides, multislides, and assemblies, Apex can create and deliver small prototypes or late runs.

Need help determining the right extension spring for your application? Contact us to discuss your needs with one of our experienced team members, or call us at 616.453.5463 to get a no-obligation quote for your company.

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