b'G Lossary oFs PrinGt erMsTerms DescriptionActive Coils The coils that are free to deflect when under load.Allow for Set Spring is supplied longer than specified to compensate for length loss when fully compressed.Angular RelationshipThe relative position of the plane of the hooks or loops of extension springs to each other.to EndsBuckling Bowing or lateral deflection of compression springs when compressed, related to the slenderness ratio (L/D).Closed Ends Ends of compression springs where pitch of the end coils is reduced so that the end coils touch.Closed & GroundSame as with closed ends, except that the end is ground to provide a flat plane.EndsClosed Length Also called Solid Height.Height of a compression spring when under sufficient load to bring all the coils into contact with adjacent coils.Close-Wound Coiled with adjacent coils in contact.erminologyCoils per Inch Also called Pitch.The distance from center to center of the wire in adjacent active coils (recommended practice is to specify number of active coils rather than pitch).Deflection Motion of spring ends or arms under the application or removal of an external load.Elastic Limit Maximum stress to which a material may be subjected without producing permanent set.Endurance Limit Maximum stress at which any given material will operate indefinitely without failure for a given minimum stress.T Free Length The overall length of a spring in the unloaded position.Gradient Also called Rate.Change on load per unit deflection, generally given in pounds per inch or Newtons per millimeter.Helix The spiral form (open or closed) of compression, extension and torsion springs.Hooks Open loops or ends of extension springs.Hysteresis The mechanical energy loss that always occurs under cyclic loading and unloading of a spring, proportional to the area between the loading and unloading load-deflection curves within the elastic range to a spring.Initial Tension The force that keeps the coils of an extension spring closed and which must be overcome before the coils start to open.Load The force applied to a spring that causes a deflection.Loops Coil-like wire shapes at the end of extension springs that provide for attachment and force application.Mean Coil Diameter Outside spring diameter (O.D.) minus one wire diameter.Modulus in Shear Coefficient of stiffness for extension and compression springs.Modulus in Tension Coefficient of stiffness used for torsion and flat springs (Youngs Modulus).Moment Also called Torque.A twisting action in torsion springs which tends to produce rotation, equal to the load multiplied by the distance (or moment arm) from the load to the axis of the spring body. Usually expressed in inch-oz., inch-pounds or foot-pounds.Open Ends. NotEnd of a compression spring with a constant pitch for each coil.GroundOpen and GroundOpen ends, not ground followed by an end grinding operation.EndPermanent Set A material that is deflected so far that its elastic properties have been exceeded and it does not return to its original condition upon release of load is said to have taken a permanent set.Pitch The distance from center to center of the wire in adjacent active coils (recommended practice is to specify number of active coils rather than pitch).Preset Full compression of a spring to solid state by manufacturer when needed to prevent length loss in operation.Rate Change on load per unit deflection, generally given in pounds per inch or Newtons per millimeter.Remove Set Full compression of a spring to solid state by manufacturer when needed to prevent length loss in operation.Residual Stress Stresses induced by set removal, shot peening, cold working, forming and other means. These stresses may or may not be beneficial, depending on the application.Set Length loss in operation due to the high stress condition of the spring.Slenderness Ratio Ratio of spring length (L) to mean coil diameter (D).Solid Height Height of a compression spring when under sufficient load to bring all the coils into contact with adjacent coils.Spring Index Ratio of the mean coil diameter (D) to wire diameter (d).Stress Range The difference in operating stress at minimum and maximum loads.Stress Relieve To subject springs to low-temperature heat treatment so as to relieve residual stresses.Shot Peened A cold working process in which the material surface is peened to induce compressive stresses and thereby improve fatigue life.Squareness of Ends Angular deviation between the axis of a compression spring and a normal to the plane of the ends.Squareness UnderSame as Squareness of Ends, except with the spring under load.LoadTorque A twisting action in torsion springs which tends to produce rotation, equal to the load multiplied by the distance (or moment arm) from the load to the axis of the spring body. Usually expressed in inch-oz., inch-pounds or foot-pounds.Total Coils Number of active coils (n) plus the coils forming the ends.Wahl Factor A factor to correct stress in helical springs effects of curvation and direct shear.190'