Every spring has two critical points of contact: its ends.
These ends aren’t just cut-and-done—they’re formed, shaped, or ground in specific ways to control how the spring performs under load, how it fits within a mechanism, and how long it will last in service.
Spring ends refer to the way the final coils of a spring are finished. This can range from a simple open coil to a precisely ground, squared surface—or specialized hooks and bends in the case of extension and torsion springs. Choosing the right end type ensures that the spring seats properly, distributes force evenly, and doesn’t fail prematurely due to stress concentrations or misalignment.
On the production floor, end finishing is one of the last—but most important—steps in the manufacturing process. Poor end design is one of the most common reasons a spring fails to function correctly after installation. That’s why Western Spring works closely with engineers to ensure each spring’s end geometry fits the application’s real-world needs—whether that’s holding tension in a medical device, rotating a latch in an aircraft cabin, or absorbing shock in agricultural equipment.
This guide walks through every major spring end type used across compression, extension, torsion, and wire forms.
Open-End Springs
- What It Is:
An open-end spring leaves the final coil in its natural pitch without bending it back toward the previous coil. The spring terminates in an open loop, with no modification or flattening. - Why It Matters:
Open ends enable a spring to compress to a shorter solid height and maintain more active coils. This allows for a more responsive spring rate in a smaller footprint—useful in tightly packed or low-load systems. It also simplifies manufacturing when squareness isn’t required. - Trade-offs:
Open-end springs can wobble or shift under compression if not supported. They’re also prone to tangling in high-volume environments and may lead to uneven load distribution if improperly seated. - Used With:
Compression Springs - Applications:
Fixtures & Jigs, Prototyping, Aerospace Sealing Systems
Ground-End Springs
- What It Is:
A ground-end spring is a closed-end spring with the final coil surface machined flat using a grinding process. This ensures both ends are perfectly perpendicular to the spring’s axis. - Why It Matters:
Grinding improves squareness and load-bearing accuracy. It prevents tilting and eccentric wear, which can dramatically extend spring life in high-cycle or precision-loaded applications. It’s especially critical in aerospace, automotive, and medical components where load paths must be exact. - Trade-offs:
Grinding adds cost and slightly reduces the spring’s overall free length. It’s also not necessary for every application—especially where the spring is fully guided or under minimal load. - Used With:
Compression Springs - Applications:
Aerospace Actuation, Medical Devices, Engine Components
Machine Hook Spring Ends
- What It Is:
Machine hooks are standard looped terminations formed at each end of an extension spring. They’re made by extending the coil wire and bending it back over itself in a semicircular form for easy attachment. - Why It Matters:
Machine hooks allow for quick installation and strong anchoring. They’re simple, cost-effective, and well-suited to repetitive tension applications where the spring is always under load. - Trade-offs:
Stress tends to concentrate at the bend point of the hook. Without proper design or stress relief, the hook can fatigue before the spring body. In high-stress environments, custom or full-loop ends may last longer. - Used With:
Extension Springs - Applications:
Appliance Mechanisms, Maintenance Systems, Agricultural Tools
Spring Crossover Hook Ends
- What It Is:
Crossover hooks are similar to machine hooks but extend across the body of the spring, crossing over its central axis. This variation reduces the spring’s profile when installed. - Why It Matters:
Crossover hooks save axial space, allowing the spring to fit into more compact designs. This is especially useful in enclosed assemblies where standard hook projections might interfere with adjacent parts. - Trade-offs:
Crossing the hook over the body can create contact points and increase wear during operation. It also limits flexibility in mounting angle and can be more difficult to install in high-speed production environments. - Used With:
Extension Springs - Applications:
Compact Medical Instruments, Defense Mechanisms, Aerospace Control Systems
Center/Side Loop Spring Ends
- What It Is:
Center and side loops are hook-style ends formed at the centerline or side of the spring’s coil. The loop direction determines the mounting orientation and tension path. - Why It Matters:
These configurations allow precise alignment during installation. Center loops provide balanced load paths, while side loops are useful when the spring must mount offset or wrap around adjacent components. - Trade-offs:
If not properly aligned with the force direction, side loops can twist or create uneven stress. Both loop styles can fatigue over time at the bend if used in high-load environments without reinforcement. - Used With:
Extension Springs - Applications:
Automotive Interiors, Medical Actuators, General Manufacturing
Full or Double Full Loop Spring Ends
- What It Is:
A full loop is a 360° hook that curves back toward the body of the spring. A double full loop adds a second loop for reinforced strength and fatigue resistance. - Why It Matters:
These designs distribute stress more evenly across the hook, dramatically improving fatigue life. They’re ideal for high-cycle applications or where springs will experience repeated tension over time. - Trade-offs:
Full and double loops require more material and space. They also increase the spring’s length and may not fit in compact housing without careful planning. - Used With:
Extension Springs - Applications:
Garage Door Mechanisms, Fitness Equipment, Tension Hardware
Reduced Loop Spring Ends
- What It Is:
Reduced loops are smaller-than-normal hook ends formed to fit over posts, inside cavities, or within tightly constrained components. They provide a compact mounting interface. - Why It Matters:
These loops are ideal for nested assemblies or precision mounting points. Their smaller footprint lets engineers reduce packaging size without compromising anchoring strength in low-load scenarios. - Trade-offs:
Their compact size limits hook flexibility, which can lead to breakage if overstressed. They also require precise alignment during assembly and are less tolerant to off-axis loads. - Used With:
Extension Springs - Applications:
Miniature Medical Devices, Aerospace Enclosures, Prototyping Rigs
Straight Leg Spring Ends
- What It Is:
In torsion springs, straight legs extend tangentially from the coil. These provide the simplest and most direct form of torque application. - Why It Matters:
Straight legs make it easy to define force direction and mounting geometry. They’re predictable, durable, and easy to install in standard brackets or pivots. - Trade-offs:
Without bends or anchoring features, straight legs may slip under load or require extra components to stay in place. They also offer limited design flexibility in tight geometries. - Used With:
Torsion Springs - Applications:
Latching Mechanisms, Medical Hinges, Rotating Shafts
Offset Leg Spring Ends
- What It Is:
Offset legs are bent away from the coil axis at specific angles or directions to allow clearance or define custom load paths. - Why It Matters:
They accommodate packaging constraints and unusual torque directions. Offset designs are common in latch assemblies or where movement must bypass nearby components. - Trade-offs:
The bends can concentrate stress and must be carefully engineered to avoid failure. These legs are also more difficult to assemble and often require custom fixturing. - Used With:
Torsion Springs - Applications:
Aircraft Panels, Tooling, Prototype Hinges
Custom or Bent Leg Spring Ends
- What It Is:
Custom leg ends are non-standard bends or shapes designed for specific mechanical needs. These can include complex curves, multi-axis angles, or flattened tabs for anchoring or actuation. - Why It Matters:
Custom leg designs allow torsion springs to interface directly with components without requiring additional brackets or parts. They enable precise torque paths and compact assemblies that wouldn’t be possible with standard leg shapes. - Trade-offs:
More complex bends require tight manufacturing tolerances and detailed engineering drawings. The custom shape may reduce fatigue life if not properly stress-relieved and can increase tooling time for small batch runs. - Used With:
Torsion Springs - Applications:
Agricultural Hardware, Precision Medical Devices, Defense Assemblies
Double Torsion Leg Spring Ends
- What It Is:
Double torsion springs use two coils wound in opposite directions, connected by a central section. Each coil has its own leg, allowing for torque in both directions simultaneously or in staged timing. - Why It Matters:
This configuration supports bidirectional forces, making it ideal for components that must return to center or hold tension in both directions. It offers symmetry and higher load capacity in confined rotational applications. - Trade-offs:
Double torsion springs are more difficult to install and require matched loading conditions to avoid uneven stress. If improperly designed, one side may dominate and reduce system life. - Used With:
Torsion Springs - Applications:
Clamping Devices, Tooling Frames, Aircraft Hatch Mechanisms
Custom Wire Form Ends
- What It Is:
Wire form ends can include hooks, tabs, loops, or any three-dimensional shape formed from wire to create functional end points for a part. These are typically used in non-helical components. - Why It Matters:
Wire form ends provide mounting, actuation, or assembly points tailored to specific product geometries. They allow spring steel or music wire parts to function as latches, clips, brackets, or connectors. - Trade-offs:
Custom shapes often require dedicated tooling and careful prototyping. Because wire forms lack the stored energy of coiled springs, they must be accurately formed to deliver mechanical performance through geometry alone. - Used With:
Wire Forms - Applications:
Medical Bracing Components, Electronics Retainers, Custom Fixtures & Prototypes
Future Trends and Innovations in Spring End Design
Spring end configurations are evolving alongside new materials, manufacturing methods, and tighter performance demands across industries. As OEMs push for miniaturization, increased cycle life, and modular component design, spring ends must adapt to support faster assembly and longer service intervals.
Several trends are shaping the future of spring end finishing:
- Micro-formed Ends:
As medical and aerospace devices get smaller, ends must be formed at sub-millimeter tolerances, often under microscope guidance or automated camera feedback systems. - Additive Forming Techniques:
Hybrid manufacturing processes are emerging that combine wire forming with 3D-printed caps, tips, or features for complex motion control or interference fit. - Integrated Coating & Forming:
Surface finishes like PTFE or antimicrobial coatings are now being applied during the end forming process to maintain cleanliness or friction control without secondary steps. - Smart Spring Integration:
Some advanced systems incorporate sensors or conductive ends into spring terminals, especially in aerospace or automotive safety systems where the spring also acts as a signal carrier.
Western Spring continues to invest in R&D and custom tooling to support the next generation of precision spring ends, meeting strict design tolerances and unique functional requirements.
