Understanding the language of spring engineering is essential when working with custom spring manufacturers, mechanical engineers, or technical design teams. This glossary of spring terminology provides clear definitions and explanations of key terms used throughout the spring manufacturing and engineering process. Whether you’re exploring materials, analyzing tolerances, or calculating fatigue, this reference guide supports better communication, accuracy, and performance. For additional information, check out the Spring Wire Properties Tables or the Spring Wire Specification Cross Reference List.
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Spring Terminology: Technical Definitions
Active Coils
The coils in a spring that are free to deflect under load and contribute to the spring’s mechanical performance.
Angular Relationship of Ends
Refers to the angular orientation between the ends or arms of an extension or torsion spring.
Baking
A heat treatment process used to reduce hydrogen embrittlement in electroplated springs.
Block
Another term for Solid Height – the fully compressed length of a spring.
Buckling
Lateral deflection of a compression spring under load, influenced by the spring’s slenderness ratio (L/D).
Close Wound
Describes springs where adjacent coils are in contact with one another.
Closed and Ground Ends
End coils that are squared and ground flat to provide a stable bearing surface.
Closed Ends
Ends of a compression spring formed to lie flat and square with adjacent coils, enhancing load distribution.
Closed Length
See Solid Height.
Coils Per Inch
Also referred to as Pitch – the distance between adjacent coils measured along the spring axis.
Deflection
The displacement or travel a spring undergoes when load is applied or removed.
Elastic Limit
The maximum stress a material can withstand without experiencing permanent deformation.
Endurance Limit
The highest stress level a spring material can tolerate for a specified number of cycles without failure.
Fixture Tempering
Tempering springs in a restrained position to improve dimensional accuracy.
Free Angle
The natural angle between arms of a helical torsion spring in the unloaded state.
Free Length
The overall length of a spring when no load is applied.
Gradient
See Rate – the change in force per unit of deflection.
Heat Setting
Pre-stressing a spring to minimize stress relaxation in service.
Helical Springs
Springs formed by coiling wire or bar stock into a helix. Includes compression, extension, and torsion springs.
Hooks
The open-looped ends of extension springs used for attachment.
Hysteresis
The energy loss during the loading and unloading of a spring, represented by the area between the load-deflection curves.
Initial Tension
The preload force required to begin separating coils in a close-wound extension spring.
Loops
Formed ends on extension springs designed for load transfer; can be machine loops, crossover loops, or custom shapes.
Mean Diameter
The average diameter of the mass of spring material, equal to one‑half the sum of the outside and inside diameters. In a helical spring, this is the equivalent to the outside diameter minus one wire diameter.
Modulus in Shear or Torsion
Also known as the Modulus of Rigidity (G), this value measures stiffness in compression and extension springs.
Modulus in Tension or Bending
Also called Young’s Modulus (E). Describes stiffness in flat springs and torsion applications.
Moment
The product of the applied force and its distance from the spring axis; also called Torque.
Natural Frequency
The lowest rate at which a spring will vibrate freely between its own ends.
Patenting
Heat treatment of high carbon wire to produce a uniform, fine-grained microstructure.
Pitch
Distance between the centers of adjacent coils in an open-wound spring.
Plain Ends
End coils with unmodified pitch – no squaring or grinding.
Plain Ends, Ground
Plain ends that are ground flat and square to improve stability.
Rate
Also called Spring Gradient – the force change per unit deflection (e.g., lbs/in).
Residual Stress
Stress remaining in the spring from cold forming, coiling, or shot peening. Can be beneficial or detrimental.
Set
Permanent deformation caused by exceeding the elastic limit.
Set Point
The stress level that causes a predetermined permanent deformation (e.g., 2% set).
Set Removal
A heat or mechanical operation to intentionally remove set before the spring is placed in service.
Shot Peening
Blasting the surface of the spring with metallic or glass media to create beneficial compressive stresses and improve fatigue life.
Slenderness Ratio
The ratio of spring free length to mean diameter (L/D). Higher ratios may increase the risk of buckling.
Solid Height
The length of a compression spring when fully compressed and all coils are touching.
Spiral Springs
Springs formed from flat strip material coiled in a planar spiral shape, loaded in torque.
Spring Index
The ratio of the spring’s mean diameter to wire diameter (D/d). Optimal range is typically 4–12.
Squared and Ground Ends
See Closed and Ground Ends.
Squared Ends
See Closed Ends.
Squareness
Deviation between a spring’s axis and its end planes. Critical for load distribution.
Stress Range
The difference between the maximum and minimum operational stress levels.
Stress Ratio
The ratio of the minimum to maximum stress in cyclic applications. Important for fatigue life.
Stress Relief
A controlled low-temperature heat treatment used to relieve residual stress without affecting spring geometry.
Torque
See Moment – rotational force applied to or exerted by a spring.
Total Number of Coils
The sum of active and inactive coils in a spring. Inactive coils include squared or ground ends.
Why Spring Terminology Matters
Understanding technical spring terminology ensures that your spring specifications, manufacturing processes, and quality standards align. Accurate communication helps reduce engineering errors, shortens lead times, and results in more efficient custom spring development.
At Wermke Spring, we work closely with engineers, buyers, and designers to turn complex mechanical challenges into simple, reliable solutions. This glossary is just one of the many spring design resources we provide to help our customers feel confident in their spring selections.
Contact Us to Learn More
Still have questions about spring terminology or need help specifying the right spring for your application? Contact Wermke Spring today at (636) 677-5500 or send us a message online. Our experts are here to help you understand your options, navigate technical requirements, and find a spring solution that fits your exact needs.
