Compression Spring Terms

Active Coils – the coils that deflect when a compression spring is under load.
Buckling – the point at which a compression spring bends when a long, slender compression spring is under load.
Closed Ends – the point at the end of a compression spring where the end coils touch.
Closed and Ground End – same as closed ends except the ends of the compression spring is ground flat.
Closed Wound – the state in which a compression spring is coiled with all adjacent coils touching.
Deflection – motion of the compression spring when placed under load.
Elastic limit – the maximum amount that compression spring wire can be placed under load before the compression spring sets.
Endurance limit – the maximum compression spring material can operate indefinitely without failure during minimum stress.
Free length – the overall length of a compression spring under no load.
Frequency – the lowest rate of vibration for a compression spring while ends are held stationary.
Hysteresis – the amount of energy lost in a compression spring during cycling.
Mean diameter – the outside diameter of a compression spring minus one wire diameter.

Modulus – the coefficient in stiffness of a compression spring.
Open ends – the same pitch throughout a compression spring
Open ends ground – same as open ends but with ground ends
Permanent set – when a compression spring is deflected beyond its elastic limit as does not return to its original position.
Pitch – the distance of one wire mean to the adjacent wire mean in a compression spring.
Rate – the change in compression spring load between units of measure.
Set removal – compressing a compression spring to its solid height to achieve desired length and reduce elastic limit.
Set – permanent distortion caused by compressing a compression spring beyond its elastic limit.
Slenderness ration – ratio of length to mean diameter in a compression spring.
Solid height – the position of a compression spring when compressed, all adjacent coils are touching.
Spring Index – the ratio of mean coil diameter to wire diameter in a compression spring.
Squareness – the angular difference between a compression spring axis and plane ends.
Total coils – the number of active coils plus the inactive compression spring coils.

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