Glossary

Those coils which are free to deflect under load. Angular relationship of ends relative position of hooks or loops of an extension spring (-Iegs of a torsion spring) to each other.

A metal composed of two or more metal elements bound together.

The angle included between the sides of the thread measured in an axial plane.

The angle between the centerlines of the ends of the bellows.

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

The American Society for Testing Materials.

The longitudinal central line through the screw.

Heating of electroplated springs to relieve hydrogen embrittlement.

The manufactured length of the bellows convolutions, with the bellows at a neutral at rest position with no applied forces acting on it.

The bellows acceptable inside diameter range for the application. This helps to define the acceptable size envelope for the bellows.

The bellows acceptable outside diameter range for the application. This helps to define the acceptable size envelope for the bellows. It is critical for tool selection and to optimize performance.

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

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

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

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

Adjacent coils are touching.

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

The number of cycles required for compression bending or offset movements. Loading is generally not a consideration here.

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.

Maximum stress which a spring can be stressed without taking a permanent set.

Maximum stress which can be repeatedly applied without incurring spring failure.

The depth of thread contact of two mated parts, measured radially.

The length of contact between two mated threaded parts measured axially.

An external thread is a thread on the outside of a fastener or similar component.

When a spring is deflected continually, the metal becomes fatigued and failure may occur at a stress level far below the elastic limit.

Number of deflection cycles until a failure occurs at a predetermined stress.

Stress at which failure occurs after a specific number of deflections.

Restraining parts during tempering to improve dimensional control.

Active power applied to a spring to cause deflection. Is erroneously called load.

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

Overall length of a spring which is not under load.

A standard for measuring material thickness.

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

A process to pre-relax a spring in order to improve stress relaxation resistance in service.

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

The angle made by the helix, or conical spiral, of the thread at a pitch diameter with a plane perpendicular to the axis.

Open loops or ends of extension springs.

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.

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

An internal thread is a thread on the inside of a member.

The distance between the centerlines of the ends of the bellows that are parallel but not on the same line.

If the part or assembly is required to be leak tested, if known, the required leak rate should be provided. The achievable leak rate will vary due to the design requirements (ID, OD, wall thickness, etc.)

Testing to determine whether the application requires the part to be leak tight (generally refers to bellows or bellows assembly).

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

The largest diameter of the thread of the screw or nut. The term “major diameter” replaces the term “outside diameter” as applied to the thread of a screw and also the term “full diameter” as applied to the thread of a nut.

If the bellows needs to be leak-tight, this is the maximum differential applied externally to the bellows, in the application.

If the bellows needs to be leak tight, this is the maximum differential applied internally to the bellows, in the application.

The term “mean area of a screw,” when used in specifications and for other purposes, designates the cross-sectional area computed from the mean of the basic pitch and minor diameters.

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.

The smallest diameter of the thread of the screw or nut. The term “minor diameter” replaces the term “core diameter” as applied to the thread of a screw and also the term “inside diameter” as applied to the thread of a nut.

(Young’s Modulus E) Coefficient of stiffness used for torsion springs 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.

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

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

If the part needs to be leak-tight, this is the differential pressure the part will be subjected to in the application. It is important to specify if the pressure will be applied internally or externally to the bellows or part.

The temperature that the part or assembly will experience during normal operation.

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

On a straight screw thread, the diameter of an imaginary cylinder, the surface of which would pass through the threads at such points as to make equal the width, the threads, and the width of the spaces cut by the surface of the cylinder. On a taper screw thread, the diameter, at a given distance from a reference plane perpendicular to the axis of an imaginary cone, the surface of which would pass through the threads at such points as to make equal the width, the threads, and the width of the spaces cut by the surface of the cone.

An element of the imaginary cylinder or cone specified under “Pitch Diameter”.

The distance from a point on a screw thread to a corresponding point on the next thread measured parallel to the axis.

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

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

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

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.

What is the desired response with pressure changes?

Maximum load at which starin or deformation is directly proportional to stress, at zero percent offset.

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

Rear-end locker springs maintain a critical constant force on the ratcheting mechanism to ensure a smooth and consistent transfer of power to the rear drive line.

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.

The surface of the thread corresponding to the major diameter of the screw and the minor diameter of the nut.

The distance a screw thread advances axially in one turn. On a single-threaded screw, the lead and pitch are identical; on a double-threaded screw the lead is two times the pitch; on a triple-headed screw, the lead is three times the pitch, etc.

The surface of the thread corresponding to the minor diameter of the screw and the major diameter of the nut.

The surface of the thread which connects the crest with the root.

A ridge or uniform section in the form of a helix on the external or internal surface of a cylinder, or in the form of a conical spiral on the external or internal surface of a cone.

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

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

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

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

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

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

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.

Ratio of mean diameter to wire diameter.

The force in pounds applied to a part and measure of stiffness under pressure.

See Closed and Ground Ends.

See Closed and Ground Ends.

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

The deformation produced by a stress as compared to the original shape.

Difference in operating stresses at minimum and maximum loads.

Minimum stress divided by maximum stress.

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

Maximum force which a material is capable of sustaining. It equals force reached divided by original cross-sectional area.

The bottom section of the thread; the greatest section between the two adjacent roots.

The distance between the crest and the base of the thread measured normal to the axis.

The distance between the adjacent sides of the thread measured along or parallel to the pitch line.

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

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

Stress point which will cause an elongation to the original length of the spring.