Spring Glossary E-G

16th February 2021

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.