ASTM - The American Society of Testing Materials.

Arbor - A round rod on a spring coiler over which wire is coiled to form a spring.

Baking - Heating electroplated springs to remove hydrogen.

Blue - A thin blue film of oxide on ferrous alloys, sometimes used to indicate that the material has been stress relieved.

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.

Closed Ends - Ends of compression springs where pitch of the end coils is reduced so that the end coils touch.

Closed and Ground Ends - as with closed ends, except that the end is ground to provide a flat plane.

Close-Wound - Coiled with adjacent coils touching.

Deflection (F) - Displacement of the ends or arms of a spring on the application of a external force (P).

Direction of Coiling - or Helix - Right or left hand as in screw system.  Should be optional, unless specifically required.

Elastic Limit- Maximum stress to which a spring can be stretched 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 failure occurs at a predetermined stress.

Fatigue Strength (Endurance Strength) - Stress at which failure occurs after a specific number of deflections.

Foot Pounds, Inch Pounds - Unit of torque in the testing of torsion springs which is equal to the load multiplied by the distance from the load to the axis of the spring.  Usually expressed in inch pounds or foot pounds.

Force (P) - Active power applied to a spring to cause a deflection. Is erroneously called load.

Free Angle - Angle between the arms of a torsion spring when the spring is not loaded.

Free Length (L) - 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. I.E.: pounds per inch.

Heat Setting - Deflecting a spring in a fixture at elevated temperatures in order to reduce loss of load at operating temperature.

Helical - Springs of spiral or cylindrical shape such as compression, extension or torsion springs.

Helix - The spiral form (open or closed) of compression, extension and torsion springs.

Hooke's Law - Load is proportional to displacement.

Hooks - Open loops or ends of extension springs.

Hydrogen Embrittlement - Hydrogen absorbed in electroplating or pickling of carbon steels, tending to make the spring material brittle and susceptible to cracking and failure, particularly under sustained loads.

Hysteresis - The difference in forces at various deflections when loading and unloading a spring.

Initial Tension (Pi) - A force wound into a extension spring during coiling to hold the coils together.

Load (Force) (P) - Active power applied to a spring to cause a deflection (F).

Loops - Coil-like wire shapes at the ends of extension springs that provide for attachment and force application.

Mean Coil Diameter (D) - Outside spring diameter (O.D.) minus wire thickness (d).

Modules in Shear or Torsion (G) - Coefficient of stiffness for extension and compression springs.

Modules in Tension or Bending (E) - Coefficient of stiffness for torsion and flat springs.

Open Ends, Not Ground - Open ends, not followed by an end grinding operation.

Open Ends, Ground - Open ends followed by an end grinding operation.

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 center of the wire in two adjacent coils.

Plain Ends - End of a compression spring with a constant pitch for each coil.

Plain ends Ground - As above followed by an end grinding operation.

Poisson's Ratio - The ratio of the strain in the transverse direction to the strain in the longitudinal direction.

Preset - The process of closing to solid height a compression spring which has been coiled longer than the desired finish length, so as to increase the apparent elastic limit.

Proportional Limit - Maximum load at which strain or deformation is directly proportional to stress, at zero percent offset.

Rate (R) (Gradient) - Change in force per incremental unit of deflection. I.E.: Pounds per inch.

Remove Set - The process of closing to solid height a compression spring which has been coiled longer than the desired finished length, so as to increase the apparent elastic limit.

Residual Stress - Stresses incorporated within a spring by coiling, compressing to remove set, shot peening, 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 limits.

Shot Peening - A cold-working process in which the material surface is peened to induce compressive stresses and thereby improve fatigue life.

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 upon 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.

Squared Ends - Refer to Closed Ends.

Squared and Ground Ends - Refer to Closed and Ground Ends.

Squareness of Ends - Angular deviation between the axis of a compression spring and a normal to the plane of the ends.

Squareness Under Load - As in Squareness of Ends, except with the spring under load.

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 Range - The difference in operating stresses at minimum and maximum loads.

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 spring 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.