Spring Glossary A-D

16th February 2021

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