Glossary of terms


  • Active Coils (n) - The coils which are free to deflect under a force.
  • Alloy - A metal composed of two or more metal elements bound together.
  • Arbor - A round rod on a spring coiler over which wire is coiled to form a spring.
  • ASTM - The American Society for Testing Materials.
  • Baking - Heating electroplated springs to remove hydrogen.
  • Brass - A copper-base alloy of copper and zinc.
  • Bronze - A copper-base alloy of copper and tin.
  • Buckling - Lateral deflection movement of a compressed spring and is related to the slenderness ratio.
  • Deflection (F) - Displacement of the ends or arms of a spring on the application of an external force (P).
  • Elastic Limit - Maximum stress which a spring can be stressed without taking a permanent set.
  • Endurance Limit - Maximum stress which can be repeatedly applied without incurring spring failure.
  • Fatigue Failure - When a spring is deflected continually, the metal becomes fatigued and failure may occur at a stress level far below the elastic limit.
  • Fatigue Life - Number of deflection cycles until a failure occurs at a predetermined stress.
  • Fatigue Strength - Stress at which failure occurs after a specific number of deflections.
  • Force (P) - Active power applied to a spring to cause deflection. Is erroneously called load.
  • Free Angle - Angle between the arms of a torsion spring when the spring is not loaded.
  • Free Length - The overall length of a spring in the unloaded position.
  • Frequency (Natural) - The number of cycles per minute at which a spring will vibrate freely once it has been excited.
  • Gauge - A standard for measuring material thickness.
  • Gradient (Rate) (R) - Change in force per incremental unit of deflection.
  • Heat Setting - Deflecting a spring in a fixture at elevated temperatures to reduce loss of load at operating temperature.
  • Helical - Springs of spiral or cylindrical shape such as compression, extension, or torsion springs.
  • Hysteresis - The difference in forces at various deflection when loading and unloading a spring.
  • Initial Tension (Pi) - A force wound directly into an extension spring during coiling to hold the coils together.
  • Load (Force) (P) - Active power applied to a spring to cause a deflection (F).
  • Modules in Shear or Torsion (G) - Coefficient of stiffness for extension and compression springs.
  • Modules in Tension or Bending - Coefficient of stiffness for torsion and flat springs.
  • Passivating - An acid dipping treatment applied to stainless steel to remove contaminants and improve corrosion resistance.
  • Permanent Set - The difference in length of a highly stressed spring upon release of a force.
  • Pitch (p) - The distance from the center of the wire in two adjacent coils.
  • Preset - The process of closing to solid height a compression spring which has been coiled longer than the desired finish length, to increase the apparent elastic limit.
  • Proportional Unit - Maximum load at which starin or deformation is directly proportional to stress, at zero percent offset.
  • Rate (R) (Gradient) - Change in force per incremental unit of deflection.
  • Residual Stress - Stresses incorporated within a spring by coiling, compressing to remove set, shotpeening, cold working or induced by heat treatment.
  • Resilience - Elastic ability of a material to rebound to its original shape after deflection.
  • Set - Permanent distortion which occurs when a spring is stressed beyond the materials elastic limit.
  • Slenderness Ratio - Ratio of spring free length (L) to the mean coil diameter (D). If the ratio is over 4.0, compression springs may buckle depending on the amount of deflection.
  • Solid Height (H) - Length of compression spring when force causes coil contact with all adjacent coils.
  • Spring Index - Ratio of mean coil diameter (D) to wire diameter (d). Best ratio is between 7-13.
  • Strain - The deformation produced by a stress as compared to the original shape.
  • Stress - The force divided by the area over which it acts.
  • Stress Relieve - Low temperature heat treatment to relieve residual stresses induced during coiling.
  • Tensile Strength - Maximum force which a material is capable of sustaining. It equals force reached divided by original cross-sectional area.
  • Torque (Movement) - A twisting force in torsion springs which tends to produce rotation, equal to the force multiplied by the distance from the force to the axis of the spring body.
  • Total Coils (N) - Number of active coils (n). For compression springs add to (n) the number of dead coils forming the ends.
  • Yield Point - Stress point which will cause an elongation to the original length of the spring.


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