Active Coils: those coils which are free to deflect under load
Angular Relationship of Ends: the relative position of the plane of the hooks or loops of extension springs to each other
Baking: heating of electroplated springs to relieve hydrogen embrittlement
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
Closed Length: see Solid Height
Close-wound: coiled with adjacent coils touching
Coils per Inch: see 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 permanent set
Endurance Limit: maximum stress at which any given material will operate indefinitely without failure for a given minimum stress
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
Gradient: see Rate
Heat Setting: fixturing a spring at the elevated temperature to minimize loss of load at operating temperature
Helix: the spiral form (open or closed) of compression, extension and torsion springs
Hooks: Open loops or ends of extension springs
Hot Pressing: see Heat Setting
Initial Tension: the force that tends to keep 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 deflection
Loops: coil like wire shapes at the ends of extension springs that provide for attachment and force application
Mean Coil Diameter: outside spring diameter (O.D.) minus one wire diameter (D)
Open Ends, Not Ground: end of compression spring with a constant pitch for each coil
Open Ends Ground: “open ends, not ground” followed by an end grinding operation
Passivating: acid treatment of stainless steel to remove contaminants and improve corrosion resistance
Permanent 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)
Rate: change in load per unit deflection, generally given in 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
Set: permanent distortion which occurs when a spring is stressed beyond the elastic limit of the material
Solid Height: length of a compression spring when under sufficient load to bring all coils into contact with adjacent coils
Spring Index: ratio of mean coil diameter (D) to wire diameter
Squared and Ground Ends: refer to closed and ground ends
Squared Ends: refer to closed ends
Stress Relieve: to subject springs to low temperature heat treatment so as to relieve residual stresses
Shot Peening: 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
Total Number of Coils: number of active coils (n) plus the coils forming the ends
