Glossary of Industrial Spring


Active Coils (n): These are the types of coils that deflect under load.

  • For squared compression springs, the total number of coils subtracted by two gives a number of active coils.
  • For extension springs, the total number of active coils equals to the total number of coils in the spring.
  • For extension springs that have hooks and threaded inserts, the total number of active coils is always lesser than the total number of coils in the spring. Loops and hooks increase the total number of active coils in a spring.

Air Spring: These springs use the elasticity of air. These springs are mostly found in vehicle suspension columns.

Angular Relationship of Ends: This refers to the relative position of the loops or hooks of extension springs.

Angle of Grind: This is the angle subtended by the spring’s ground end surface.

Arbor: This can be a shaft, or round hard rod, on which springs are wound. It is also known as a mandrel.

Allow for Set: This term is applied to bulk orders. The spring supplied measures longer than the specified length to avoid loss of length during compression. However, compression may occur during the final stage of assembly.


Baking: This is the method of heating springs to relieve hydrogen absorbed during the electroplating process.

Balance Spring: This is a type of spiral torsion spring used in various devices, where the electricity is partially transferred to rotating devices without affecting the rotation. This spring is also known as hairspring.

Belleville Springs: These are the frusto-conical shaped springs, which are used to apply a flexible load to a bearing, or a bolted joint. The springs have various beneficial load-deflection characteristics. These disc-shaped springs are also referred as Belleville washers.

Blue: This is a thin blue film of oxide drawn on ferrous alloys to indicate the material is stress-free.

Buckling: This refers to the lateral deflection, or bowling of compression springs, relative to the slenderness ratio when it is compressed.


Cantilever Springs: These springs are clamped at one end when the force is applied on the other end. The cantilever springs may be round, square edged, milled, or precision machined as per the requirement.

Closed Wound, or Close Ends: These springs have closely wound coils with reduced pitch. In these springs, the adjacent coils touch other.

Closed and unground Ends: This term is synonymous with compression springs with closed and square ends, or squared ends. These springs have ends with zero pitches.

Closed and ground ends: This term is used for compression springs with squared and ground edges, and pitches reduced to zero and squared with the spring axis.

Compression Springs: These are springs are designed to compress under the load. The loops of compression springs don’t touch each other in unloaded position, and they require no attachment points. Round wire compression springs store more energy than rectangular compression springs.

Constant Springs: In these springs, the supported load will remain constant throughout the deflection cycle.

Constant-force Springs: These springs exert constant force over a range of motion. The constant-force springs are made from rolled ribbons of spring steel.

Compressive Stress: This is the state of stress when the material tends to compress (decrease in volume). This type of compression is usually induced by the pushing forces on the spring. Most springs are designed to counter the compressive stress.

Closed Length: Same as Solid Height.

Creep: This refers to the change in the length of a spring when a constant force is applied.

Coils per Inch: Same as “Pitch”.

C-Type Eccentric Retaining Ring: This is a C-shaped eccentric retaining ring, available in two types: for in-bore and for one-shaft use.

C-Type Concentric Retaining Ring: This a C-shaped concentric retaining ring, available in two types: for one-shaft and for in-bore use.

Ceramic Spring: These are springs made from ceramic material. Ceramics are sintered materials with aluminum oxide.

Circlip: This is a very popular term for circular springs such as C-type retaining rings.

Cold Formed Springs: These springs are formed at a low temperature. The examples include cold formed coil extension springs and cold formed compression springs.

Combination Springs: This refers to the multiple springs that are stacked to obtain certain characteristics. These springs may be combined parallel or serially.  A combination featuring two springs is called a parallel double spring, or a serial double spring.

Composite Resin Springs: The term refers to any spring made from composite resin material.

Constant Rate Springs: This refers to the spring deflection, which is linear to the load applied.


Deflection (F): Deflection is the movement of spring arms or ends, when an external load (P) is applied to or removed from the spring.

Direction of Wind: Direction of wind is associated mainly with the torsion springs. This direction can either be left hand wind or right hand wind. When load is applied, the spring should rotate in the same direction as it is coiled.


Elastic Limit: Spring is elastic and regains its original shape when the applied force or pressure is released. Elastic limit is the maximum amount of deflection that a spring can attain safely without deforming permanently.

 Elastic Modulus: This is a number that determines the stiffness of a material. It determines the resistance that a material offers, when a force is applied to it.

 Elastic Deformation: It is a reversible change of shape. In other words, it is a spring-like deformation, where the material regains its original shape after the applied force is released.

 Endurance Limit: Maximum stress that a material can survive unfailingly for a minimum stress given. It is also referred to as fatigue limit or fatigue strength.

 End Style – Crossover: It is a type of end style formed by wire crossing over from the center of the spring and forming a circle for the end.

 End Style – Machine: It is a type of end style of an extension spring formed, when the wire comes directly off the body and forms a circle through the center for the end.

 End Style – Side: It is a type of end style of an extension spring formed when the wire forms a circle at the outer diameter for the end.

 End Type – Double Loop: It is a type of extension spring’s end formed by two coils. In this end type, there is no gap between the end of the wire and the coils.

 End Type – Hook: It is a type of extension spring’s end formed by only one coil. In this end type, there is a gap between the end of the wire and the coil.

 End Type – Single Loop: It refers to an extension spring end featuring only one coil. In this end type, there is no gap between the end of the wire and the coil.

 Ends – Closed Not Ground: The pitch of the end coils is lowered. Thus, the ends of the coils touch.

 Ends – Closed And Ground: It is similar to the “closed not ground ends”, but the end is ground, and provides a flat plane.

 Ends – Open Not Ground: These are compression springs’ ends having a pitch for each coil. The last coils do not touch.

 Ends – Open And Ground: This is similar to “open not ground ends”. The only difference is that it is followed by an end grinding operation.

 E-Type Retaining Ring: This retaining ring has a shape of the English alphabet ‘E’, hence the name. This type of ring is mainly used in on-shaft applications.

 Extension Spring: Extension spring is a type of spring, which absorbs and stores energy. It resists a pulling force applied to it. Round wire is used to manufacture this spring, and is generally close wound. The spring has some initial tension applied to it.


Fastener Spring: These springs are used for fastening applications, and come in various shapes and sizes based on the application.

Fatigue: It is the structural damage that is caused during a course of continuous cyclic loading. Incessant loading and unloading causes the material to weaken, resulting into fatigue.

 Fixture Tempering: Also referred to as flattening, fixture tempering is a process carried out under pressure. This process helps remove distortion, and improve dimensional control.

 Flat Spring: These springs get the name from their shape. They are flat, and can store or release energy, when deflected by an external load. These springs are also referred to as leaf springs and are used in the suspension system of wheeled vehicles.

 Fluid Spring: These are special types of springs, which use the elasticity of gas or liquid. These spring devices have fluids filled in them that are compressed mechanically, when an external force is applied. On releasing this force, spring output is yielded, and the spring regains its original position.

 Formed Wire Spring: These are springs having different shapes. They are made from different wire materials.

Fracture: This term refers to the breakage of a material in two or more pieces, when excess stress is applied to it.

Free Angle: It is the angle formed between the arms of a torsion spring. This angle is formed when the torsion spring is not loaded.

 Free Length (L): Free length is the actual length of a spring, when no external force or load is applied to it.

 Frequency (Natural): Frequency is the minimum natural rate of a spring’s free vibration, when its ends are restrained. Generally, it is calculated in cycles per second.


Gas Pressure Spring: Unlike a regular metal spring, a gas spring is a special type of spring that uses compressed gas filled in a cylinder to exert force. The gas is compressed with the help of a piston. These springs are also referred to as gas springs.

 Gradient: It is also referred to as Rate (R), which is calculated as change in load per unit deflection. Generally, the gradient is measured in pounds per inch (N/mm).

 Grip Ring: Grip rings are special types of rings that are used to hold casters firmly to an item. They are retaining rings that squeeze when pushed into a hole, and expand on releasing, thus making a firm hold of the item. These rings are mainly used for shafts that do not have grooves.

 Ground Ends: These are the ends of a spring that are ground for providing a flat plane.


 Heat setting: Heat setting is the process of fixing the spring at higher temperature, in order to regulate the loss of load at running temperature. It provides dimensional stability, along with stretchability and softness to the material.

Helix: It is any curve in 3D space, where the tangent line at any point makes a constant angle with a fixed line. The fixed line is called the axis.

Hooks: Hooks are pieces of metal/plastic having a curved bent at some definite angle. They are used for catching, pulling, holding, or suspending objects.

Hot Wound Spring: Hot wound springs are also known as hot coil springs.  They are made from a spring material with a diameter of 1/2 inch and above. Such springs are widely used in various automotive and railroad equipment.

Hydrogen Embrittlement: Hydrogen embrittlement is the process of diffusing hydrogen into metals, which causes fracture and brittleness, particularly under sustained loads. It helps in reducing the ductility and load-bearing capacity of a metal.

 Hysteresis: Hysteresis is defined as the energy loss which occurs during the cyclic loading and unloading of a spring. It is proportional to the area within the elastic range of a spring.

Hydropneumatic Spring: Hydropneumatic spring is a spring that uses a gas cushion spring or a liquid accumulator spring, and offers no natural roll stiffness.


Initial tension: To prevent the coils of an extension springs from getting closed, a force is applied, which is referred to as initial tension.


Leaf Springs: These springs consists of flat bars in varying lengths, which are clamped together to improve resilience and efficiency. Railway and automotive leaf springs are the two popular types.

Load: This refers to the force applied to the spring causing deflection.

Lock Washers:  These are designed to apply a spring force against a bolt or a nut.

Loops: These are coil-wire shape configurations with minimal gaps, generally found at the end of extension springs. The loops allow force application and attachment.

Linear Load Deflection: This term is used when deflection is proportional to load.


Magnetic Spring: This spring use the magnetic forces of attraction and repulsion.

Mean Coil Diameter (D): The average diameter of the mass of spring is calculated as half-sum of the inner and outer diameters. In a helical spring, this value can be obtained by subtracting outer wire diameter by one wire diameter.

Mechanical Spring: These are elastic springs, which distort, deflect, or absorb energy when load is applied. The springs will regain their original shape when released.

Metallic Spring: This is any spring made from a metallic material. The springs are referred by their material of construction such as steel springs, copper springs, etc.

Modulus in Shear or Torsion (G): This refers to the coefficient of stiffness used for compression and extension springs.

Modulus in Bending or Tension (E): This refers to the coefficient of stiffness used for flat and torsion springs.

Modulus of Elasticity: See Young’s Modulus

Modulus of Rigidity: See Shear Modulus

Moment: See Torque

Mainspring: These ribbon shaped springs are used as a power store in watches, music boxes, and clocks.


Natural Frequency: This refers to the lowest rate of free vibration of a spring that is vibrating between its own ends.

Negator Spring: This is a thin metal band with a slight concave cross-sections. The spring adopts a flat-cross section when coiled, and returns back to its curve when unrolled. It produces constant force throughout the displacement and nullifies any re-winding tendency. The most common application is the retracting steel tape.

Nonferrous Metal Spring: This term is used for any spring made from a non-ferrous metal.

Non-Metallic Spring: The spring made from non-metallic material is known by this name.

Nonlinear Spring: The spring where the deflection is not proportional to the load applied.

Nonlinear Load Functions of Springs: This refers to the set of functions like absorbing energy, mitigating shock, applying a definite torque or force, supporting masses in motion, or isolating vibrations, indicating or controlling torque or load.


Open Ends, Ground (OEG): This is end of a compression spring, where all coils have a constant pitch, but grinding is performed on the end coil.

Open Ends, Not Ground (OENG): This is end of a compression spring, where all coils have a constant pitch, and the end coils are not touching coils lying adjacent.

Overall Length: This is the measure of an extension spring in the unloaded position from the top to end.

Operating Travel: This distance is subtracted from the length of spring after applying the operating force.


 Passivating: Passivating is a process in which stainless steel is treated with an acid. This process helps remove the contaminants from the material, thus improving the corrosion resistance of the material.

Patenting: Patenting is a process in which carbon steel is heated above its critical temperature. The heated carbon steel is then cooled at a controlled rate. This process helps achieve a fine, and pearlitic microstructure.

 Permanent Set: When a material is exposed to an extensive external force or load for a long time, it starts losing its elastic properties. A point is reached, after which the material gets permanently deflected, and does not regain its original position upon removal of applied force or load. This condition is referred to as a permanent set.

Pitch (p): Pitch is the total distance measured from the center to the center of wire in neighboring active coils. Generally, it is recommended to mention the number of active coils instead of pitch.

Plain Ends: This refers to the end coils of a compression spring that have a constant pitch. These ends are not squared.

Plain Ends, Ground: Plain ends and ground refers to the end coils of a helical spring that have a constant pitch. The wire ends of the coils are ground square with the axis.

Pneumatic Spring: These are a type of fluid springs. The springs make use of compressed air to exert force.

 Poisson’s Ratio: Poisson’s ratio is the ratio of transversal expansion to axial compression. It is denoted by μ or ν (nu).

 Preset or Remove Set: Preset, which is also referred to as removal set is the condition of a spring, when it is fully compressed to solid state by manufacturer. This is done to avoid length loss during operation.

Progressive Rate Spring: Progressive rate spring, which is also referred to as linear or straight rate spring, is a special type of spring that can exhibit multiple rates.

Plastic Deformation: Plastic deformation is the permanent deformation of a spring or a material. The applied force changes the shape of the material or spring permanently.


Rear-end Locker Springs: Rear-end locker springs are also referred to as differential lock springs. These springs are mostly used in vehicles in the differential lock hub. This helps bring the lock hub to its original (inactive) position, once the front wheels of the vehicle are engaged and disengaged from differential and drive shafts.

 Relaxation: Relaxation is the state, which is exactly opposite to that of tension or stress.

 Residual stress: A residual stress is a kind of stress that resides in a material, even after the externally applied force, or the cause of stress has been removed. This stress can either be desirable or undesirable, useful or useless, depending on the application.

Retaining Ring: Retaining ring is a circular spring, which is specially designed to stop the axial movement. The ring snaps into the groove that is designed on the shaft. In case of shafts without grooves, a grip ring is used, which is also a type of retaining ring.

Rubber Spring: As the name suggests, these springs make use of rubber material for spring action.


Set: When the material of a spring is distorted to an extent beyond its elastic limit, it causes permanent distortion. This is referred to as set.

 Shaft: Shaft is a parameter, which determines the maximum diameter that a spring can have in different industrial applications.

 Shear Modulus G: Shear modulus, which is also referred to as the modulus of rigidity, is the ratio of shear stress to the shear strain.

 Shear Strain: Shear strain is the strain that is produced, when there is a change in a body’s shape or deformation without any change in the volume.

 Shear Stress: Shear stress is the component of stress. It is the stress that is caused as a result of an applied force. This force produces sliding failure of the material along a plain, which is parallel to the applied force’s direction.

 Shot Peening: Shot peening is a process for metal finishing. It is a cold work process, where the surface of the material is peened to prevent fatigue and stress corrosion failures. This process also helps increase the fatigue life of the product.

 SI: SI, which is also referred to as a metric system, is an International System of Units.

Slenderness Ratio: Slenderness ratio is defined as the ratio of spring length (L) to the mean coil diameter (D).

 Snap Ring: Snap ring is similar to a retaining ring. Snap ring is a circular spring, which is used to restrain the axial movement. The ring is snapped into the groove designed on the shaft.

 Solid Height (H): Solid height of a spring is the height, when all the adjacent springs are touching. It is the height at which the spring cannot exert any more force.

 Spiral Springs: As the name suggests, these springs are made by coiling the wire in spiral or helical form. Spiral springs are used in applications such as galvanometers, watches, etc.   These springs have torque loaded about the axis, which is normal to the spiral plane.

 Spring: A spring is an elastic mechanical device, which when pressed or pulled, returns to its original position and shape.

 Spring Index: Spring index is defined as the ratio of mean coil diameter (D) to wire diameter (d).

Spring Rate (R): It is the amount of load needed to compress a spring. The spring rate defines the resistance of a spring in working condition. It is denoted by R and is measured in 1 DaN/mm = 10 N/mm.

Spring Washer: This subtype of washer is also referred to as a disc spring. A spring washer has a capability to exert compensating force, which helps absorb a shock, or sustain a load.

 Squared and Ground Ends: See Closed and ground ends.

 Squared Ends: See Closed ends.

 Squareness of Ends: Squareness of ends is defined as the spring’s perpendicularity to its axis. The squareness of ends of the spring can be measured by placing it on a flat surface. A black plate is set at a right angle to the flat surface.

 Squareness Under Load: It is similar to the squareness of ends, but in this case, the spring is under load.

 Static Loading: Static loading is a process of steadily loading springs with load less than 1000 times. Static loading helps determine the maximum load that a spring can take.

 Stiffness: Stiffness is defined as the resistance that an elastic body offers when an external force or load is applied to it.  It is generally measured in N/m.

 Strain: When a solid material is under a continuous stress, it causes deformation, which is referred to as strain. In other words, the change in shape or size of a material is known as strain.

 Stress: Stress is defined as an external force exerted on an object or a material. In the US customary units, it is typically measured in Pounds per Square Inch (PSI). Pascal (Pa) is the SI unit of stress.

 Stress Range: Stress range is the difference between the operating stress at minimum load and maximum load.

 Stress Ratio: It is the ratio of minimum stress to the maximum stress.

Stress Relieve: This is the process in which a spring is subject to low temperature heat treatment. This relieves the spring of any residual stress.


 Tensile Strength (Rm): Tensile strength is the maximum stress that a material can survive before it gets deformed permanently or breaks. Thus, materials that have a high tensile strength last long, and are difficult to break.

 Tensile Stress: Tensile stress is also referred to as tension, and is defined as the state of a material, which leads to expansion. This expansion is caused due to the axially directed pulling forces applied to the material. In this expansion, the volume of the material remains the same as original. The stress on the material due to applied force is termed as tensile stress.

Tension Spring: As the name suggests, a tension spring is capable of operating with a tension load. This spring is also referred to as extension spring. As you go on applying load, the spring stretches.

 Torque (M): The amount of force that causes a body to rotate is termed as torque. It is measured in Newton meters (Nm). It is calculated by multiplying the load with its distance from the axis of the spring.

 Torsion Spring: Torsion spring is a type of spring that stores mechanical energy when twisted. In a twisted state, this spring exerts an equal and opposite force.

 Total Number of Coils (Nt): Total number of coils is determined by adding the total number of active coils (Na) to the coils that form the ends.

Trapped Stress: Trapped stress is the other name for residual stress. It is the stress that stays in an object, even after the stress causing force is released.


Variable rate springs: Variable rate springs are the type of springs that change stiffness as they deflect. Such springs use coils of varying thicknesses and spacing, and help compensate weight changes.

Volute Springs: These are the compression springs made in the shape of a cone to avoid coils from touching each other under compression.

V- Springs: The springs are named after their shape, and are used in antique firearms such as flintlock, Wheelock, and percussion cap locks.


Waved Spring Washer: Waved spring washers is made by shaping wire into a wave pattern. These spring washers are used in thrust loading applications with limited axial space. The waved spring washers serve as a cushion between different parts of the machine assemblies, and help reduce friction.

Waved Washer: Waved washers are useful in moderate thrusting of load within limited radial space. The washer is made with a thin plate, and wavy patterns are formed on it.

Wire Forming: Wire forming is the process of bending or reshaping any wire under the action of a constant force which alters its real length. These wires are designed to obtain high tolerance and design.

Wire Spring: Wire springs are made from coiled wire, which helps in storing and releasing energy. It is typically composed of 18% chromium and 8% nickel.

Wahl Factor: Wahl factor is also known as the stress factor, which describes the effect of direct shear and change in coil curvature.

Wave Springs: This term refers to number of wave shaped washers, springs, and expanders. These springs are made from flat wire, and are marcelled by die stamping, into a wavy pattern.


Yield strength: The stress at which the material exhibits specified deviation to deform from plastic shape to elastic shape. It serves as an upper limit for the allowable stress in context of precise dimensional tolerance.

Young’s modulus: Young’s modulus determines the stiffness of the given material when the substance is being deformed elastically under the action of any force. It is the reciprocal of stress upon strain.