Spring Glossary E-G

Effective Coils

See the definition for active coils here.

Elastic Limit

The point at which a spring will become permanently deformed due to the stress. The elastic limit is a function of the spring’s material, the number of coils, the length of the spring and the tightness of the wind.


A zinc coating of steel to prevent oxidisation. The spring material is placed in a solution containing zinc at a high temperature. Typically, at 450 degrees C

Extension Spring

A spring designed to provide resistance against extension.


In the case of spring manufacture this is a term used to describe the gradual wearing of spring material over long use periods. Micro fractures in the spring material occur under load and increase in severity over time. The fatigue process can be accelerated by processes such as oxidisation and be mitigated by strengthening the original spring material and by aging and hardening the springs material to provide stronger molecular bonds.

Fitted Length

The length of a spring when assembled into the position, within a mechanism, from which it is required to function. This will often vary from the resting or manufactured length as allowances are made for springs to extend or compress under load.

Free Angle.

A torsion spring is a spring where the spring ends are open and extend at a tangent from the main body. Typically, at 90 degrees from each other. The springs body provides resistance to these ends preventing them from being easily compressed (the angle between them decreased under pressure) or extended (the angle between the legs increases under load). The free angle is the angle between the legs of a torsion spring when the spring is not loaded.

Free Length

The length of a spring when it is not loaded. In the case of extension springs this includes the anchor points.


Gauge has two distinct meaning. Gauge of material. The thickness of the material used in constructing a spring. It can also refer to the device used to measure aspects of the spring. You may use a gauge such as a digital caliper to measure the gauge of spring material.


The removal of metal from the end faces of a spring by the use of abrasive wheels to obtain a flat surface, which is square with the spring axis.

Ground Ends

The end of a spring is ground to provide a flat plane. Handing The direction in which the helix of a spring is formed.


Active Coils

A term for coils under tension. Those coils of a spring that are actively under tension, stress, or load at any point of their use.

This can be roughly calculated by dividing the length of the body by the diameter of the spring then subtracting one.


The heating and setting process of the material of a spring so that the molecular structure is as evenly distributed as possible reducing the chances for weak spots.

Allowing for Set

A spring is supplied slightly over sized when used in a compression situation allowing for the settling of the spring material under stress.


Distortion of the spring, typically  along its length. This can happen when a spring under load exceeds its tolerances.


An incomplete circle of material designed to resist extension used to clip or clamp an object. Pressure applied to the flanges opens the clip and the resistance in the material closes and fixes it. A commonplace example to help illustrate this might be the clips around a downpipe from a roof gutter.

Closed End Spring

A spring where the helical pattern of the main body of the spring is compressed or reduced giving a much tighter radius on the final coil. Closed end springs may also be ground in this final circuit to provide a flatter surface for contact to provide more stability.

Closed Length

Similar to close ends, in this case the final turn is reduced tightening, flattening and sometimes grinding so that at the end of the last diameter the spring is at the same height as the start of the final diameter.


A spring material wound in  helix around a central axis (actual or geometric). Each complete diameter is called a coil. Often forming a cylinder or, if tapered with decreasing or increasing  diameters a cone.

Compression Spring

Using coils as described above, constructed to resist compression. The load they can effectively withstand is a function of the number of coils, the material the spring is constructed from and the diameter of each coil.

Conical Spring

A spring where the diameter around the central axis increases or decreases along its length forming a cone shape.

Dead Coils

Coils, often at the beginning or end of a spring that do not contribute to its rate of extension or expansion. Most often used to provide stability and increase the length between a springs anchor points without introducing greater stress to extended (active) coils.

Spring Displacement

(Thanks to softschools.com for this succinct definition)

According to Newton's Third Law of Motion, as a spring is pulled, it pulls back with a restoring force. This force follows Hooke's Law, which relates the force of the spring to the spring constant, and the displacement of the spring from its original position.

force of the spring = -(spring constant k)(displacement)

F = -kx

F = restoring force of the spring (directed toward equilibrium)

k = spring constant (units N/m)

x = displacement of the spring from its equilibrium position



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