Active Coils Those coils which are free to deflect under load.

Angular Relationship of Ends Relative position of hooks or loops of an extension spring (or ends of a torsion spring) to each other.

Baking Heating of electroplated springs to relieve hydrogen embrittlement.

Block See Solid Height.

Buckling Bowing or lateral displacement of a compression spring. This effect is related to slenderness ratio L/D.

Close Wound Adjacent coils are touching.

Closed and Ground Ends Same as Closed Ends, except the first and last coils are ground to provide a flat bearing surface.

Closed Ends Compression spring ends with coil pitch angle reduced so they are square with the spring axis and touch the adjacent coils.

Closed Length See Solid Height.

Coils Per Inch See Pitch.

Chrome Silicon (wire) Alloy of steel, stronger than Oil Tempered wire.

Compression Spring A spring which derives its usefulness because it pushes against a load which makes it smaller.

Dead Coil A coil of wire which does not contribute to the motive force of a spring. In extension and torsion springs, there are no dead coils. In compression springs, the coils at each end that lay against each other are dead coils: all the rest are active coils.

Double Torsion A form of torsion spring that has two coils; one left-handed and one right-handed, connected by a central tongue.

Deflection Motion imparted to a spring by application or removal of an external load.

Elastic Limit Maximum stress to which a material may be subjected without permanent set.

Endurance Limit Maximum stress, at a given stress ratio, at which material will operate in a given environment for a stated number of cycles without failure.

Extension Spring A spring which derives its usefulness because it pulls against a load which makes it longer.

Fixture Tempering Restraining parts during tempering to improve dimensional control.

Free Angle Angular relationship between arms of a helical torsion spring which is not under load.

Free Length Overall length of a spring which is not under load.

Gradient See Rate.

Helical Springs Springs made of bar stock or wire coiled into a helical form. This category includes compression, extension and torsion springs.

Hooks Open loops or ends of extension springs.

Hysteresis Mechanical energy loss occurring during loading and unloading of a spring within the elastic range. It is illustrated by the area between load-deflection curves.

Initial Tension A force that tends to keep coils of a closewound extension spring closed and which must be overcome before the coils start to open.

Loops Formed ends with minimal gaps at the ends of extension springs.

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 (Modulus of Rigidity G) Coefficient of stiffness used for compression and extension springs.

Modulus in Tension or Bending (Young’s Modulus E) Coefficient of stiffness used for torsion or flat springs.

Moment A product of the distance from the spring axis to the point of load application, and the force component normal to the distance line.

Music Wire A high-carbon steel alloy used in making springs.

Natural Frequency Lowest inherent rate of free vibration of a spring vibrating between its own ends.

Passivate (-ation) The process of removing chemical coatings from stainless steel by immersion in an acid bath.

Patenting The process of heating carbon steel above its critical temperature and cooling at a controlled rate to achieve a fine pearlitic microstructure.

Pitch Distance from center to center of wire in adjacent coils in an open?wound spring.

Plain Ends End coils of a helical spring having a constant pitch and ends not squared.

Plain Ends, Ground Same as Plain Ends, except wire ends are ground square with the axis.

Rate Spring gradient, or change in load per unit of deflection.

Residual Stress Stress mechanically induced by such means as set removal, shot?peening, cold working, or forming. It may be beneficial or not, depending on the spring application.

Set Permanent change of length, height or position after a spring is stressed beyond material’s elastic limit.

Set Point Stress at which some arbitrarily chosen amount of set (usually 2%) occurs. Set percentage is the set divided by the deflection which produced it.

Set Removal An operation which causes a permanent loss of length or height due to spring deflection.

Shot-Peening Blasting the surfaces of spring material with steel or glass pellets to induce compressive stresses that improve fatigue life.

Slenderness Ratio Ratio of spring length to mean diameter L/D in helical springs.

Solid Height Length of a compression spring when deflected under sufficient load to bring all adjacent coils into contact – no additional deflection is possible.

Spiral Springs Springs formed from flat strip or wire wound in the form of a spiral, loaded by torque about an axis normal to the plane of the spiral.

Spring Index Ratio of mean diameter to wire diameter.

Squared and Ground Ends See Closed and Ground Ends.

Squared Ends See Closed Ends.

Squareness Angular deviation, between the axis of a compression spring in a free state and a line normal to the end planes.

Stainless Steel (wire) An alloy used in making springs that will not rust. The most common stainless steels are called 302 and 17-7.

Stress Range Difference in operating stresses at minimum and maximum loads.

Stress Ratio Minimum stress divided by maximum stress.

Stress Relief A low temperature heat treatment given springs to relieve residual stresses produced by prior cold forming.

Torque See Moment.

Torsion Spring A spring which derives its usefulness by trying to return to its original shape when subjected to a load traveling around its axis.

Total Number of Coils
 The sum of the number of active and inactive coils in a spring body.

Variable Pitch A form of compression spring that has more than one pitch.