Frequently Asked Questions

What is the difference between a compression and an extension spring?
A compression spring shortens under load. It stores energy when squeezed and pushes back. An extension spring lengthens under load. It stores energy when pulled apart and pulls back.
Compression springs have open coils with space between them. Extension springs have tightly wound coils and usually end in hooks or loops.
They are not interchangeable. Using a compression spring in tension damages the end coils. Using an extension spring in compression causes it to buckle and lose its initial tension.

What is the difference between a tension spring and a torsion spring?
“Tension spring” is simply another name for an extension spring — it works in a straight line under pull. A torsion spring works by twisting around its axis and stores rotational energy.
The names sound similar, but the geometry, loading direction and replacement parts are completely different. If a parts list says “tension spring”, it almost always means an extension spring. Check the application: if the load is rotational (hinge return, clothes peg, etc.), you need a torsion spring.

What are the four main types of springs?                                                                                                                                                                                     In general engineering the four core families are compression, extension, torsion and constant-force springs. Specialty types include disc (Belleville), wave, leaf, gas and clock/spiral springs.
When the question refers specifically to vehicle suspension, the four common types are coil, leaf, torsion bar and air springs.

Are coil springs and helical springs the same thing?
Yes. “Helical” describes the geometry (wire wound in a helix); “coil” is the everyday term for the same thing. Compression, extension and torsion springs are all helical (coil) springs. They share the same basic shape but are loaded differently. In every helical spring the wire itself is twisted about its own axis as the spring deflects — that torsional stress is what stores the energy.

What is spring rate and how do I calculate it?
Spring rate (k) is the force required to deflect the spring by one unit of length (normally expressed in N/mm). Hooke’s law states F = kx.
To measure an existing spring, apply a known load, measure the deflection and divide force by deflection. Check at two or three load points to confirm the spring is still in its linear range.
If you know wire diameter, mean coil diameter, number of active coils and the shear modulus of the material, you can also calculate the rate from the standard spring formula.

Why does a torsion spring have a wind direction?
A torsion spring is designed to be loaded in the direction that winds the body tighter. Loading it the opposite way unwinds the coils, causes rapid fatigue and drastically shortens service life.
Right-hand-wound springs are loaded clockwise (looking at the open end); left-hand-wound springs are loaded anti-clockwise. Always confirm wind direction before substituting a spring.What is the most common type of spring failure?
It depends on the type: Extension springs usually fail at the hook bend (a classic stress-concentration point). 
Compression springs commonly take a permanent set (become shorter) when overloaded, or suffer surge fatigue at high cycle rates. 
Torsion springs typically fracture at the leg-to-body transition, especially if loaded in the wrong direction.
In most cases the body coils still look perfect when the spring has already failed.

Are Belleville washers and disc springs the same thing?
Yes. Belleville washer, disc spring, conical disc washer and cup washer all refer to the same family — a slightly conical disc that flattens under axial load. They produce high force in a very short space and can be stacked (in parallel for more force, in series for more travel) to tailor the load-deflection curve. Industrial sizes are covered by DIN 2093.

Can I use a compression spring as an extension spring?
No. Compression springs have open coils and no hooks. Pulling on the ends distorts the end coils and ruins the geometry.
If you need to reverse the direction of load, use a drawbar spring (a compression spring with an internal pull rod that converts compression into a controlled tension force with a built-in maximum extension).

What’s the difference between a gas spring and a coil spring?
A gas spring uses pressurised nitrogen and oil inside a sealed cylinder. It delivers near-constant force over most of its stroke and has built-in damping. A coil (helical) spring relies on elastic deformation of metal wire, so force rises linearly with deflection.
Gas springs are ideal where you want constant lift force (bonnets, tailgates, machine covers). Coil springs are used when force should increase with deflection.

What material is best for a corrosion-resistant spring?
For most corrosive environments, 316 stainless steel (A4) is the standard choice — it offers better chloride resistance than 304/A2. For severe or salt-water duty consider 17-7 PH stainless or nickel alloys. For high-temperature corrosive service, Inconel X-750 is often specified.
Note that stainless springs have lower tensile strength than carbon-steel springs, so they usually need to be physically larger (thicker wire or more coils) to carry the same load.

What measurements do I need to send AIMS for a custom spring quote?
Compression or extension spring: free length, wire diameter, OD, ID, end/hook type, and either the spring rate or the load required at a given height.
Torsion spring: wire diameter, OD, body length, leg lengths, free angle between legs, and wind direction (LH or RH).
Also tell us the application, operating environment (temperature, wet/dry, chemicals), expected cycles, preferred material and finish, and quantity. A clear photo of the original or broken spring is usually more useful than a sketch.How do I measure a spring for replacement? Compression: free length, OD, wire diameter, total coils, end type (closed & ground / closed unground / open). 
Extension: body length (excluding hooks), OD, wire diameter, body coils, hook type and gap. 
Torsion: body length, OD, wire diameter, number of coils, each leg length, free angle, and LH/RH wind.
Use vernier calipers or a micrometer for wire diameter — a steel rule is not accurate enough.

What is a constant-force spring used for?
Constant-force springs produce a nearly constant pulling force no matter how far they are extended. Typical applications include retractable cords (vacuum cleaners, hair dryers, fall-arrest reels), tape measures, window counterbalances, motor brushes (maintaining contact pressure as the brush wears) and self-retracting machine guards.

What is the difference between a torsion spring and a torsion bar?
Both store energy by twisting, but the geometry is completely different. A torsion bar is a straight rod twisted about its long axis (used in some vehicle suspensions and anti-roll bars). A torsion spring is a coiled spring with two legs that is loaded rotationally around the coil axis. They are not interchangeable. 
Need the right torque value? Our Metric Bolt Torque Chart covers every common grade and size.

What is the difference between ASTM A227 and ASTM A229 spring wire?
Both are carbon-steel spring wires, but they differ in processing and performance.
ASTM A227 (hard-drawn) is cold-drawn and economical — suitable for general static-load springs.
ASTM A229 (oil-tempered) is heat-treated after drawing, giving better fatigue resistance and a higher continuous service temperature (≈150 °C vs ≈120 °C for A227).
For springs that cycle repeatedly (valve springs, latches, etc.), choose A229. For purely static applications where cost is critical, A227 is adequate.

Why is music wire (ASTM A228) the default spring material?
Music wire offers the highest tensile strength of any standard carbon-steel spring wire (typically 1 900–2 700 MPa depending on diameter). It is drawn from high-purity, high-carbon steel, so a music-wire spring stores more energy per unit volume than an equivalent hard-drawn or oil-tempered spring. Consistency from batch to batch is also excellent.
Trade-offs: it is not suitable for corrosive environments or temperatures above ≈120 °C, and it costs more than A227. Most light-to-medium industrial compression and extension springs are made from music wire unless corrosion or temperature dictates otherwise.

Why do stainless-steel springs have lower load capacity than carbon-steel springs of the same size?
Stainless spring wire (ASTM A313) has both a lower shear modulus (G ≈ 69–73 GPa vs ≈80 GPa for carbon steel) and lower achievable tensile strength. The lower modulus reduces spring rate; the lower strength reduces maximum allowable stress and therefore maximum load.
To match the performance of a carbon-steel spring, a stainless spring usually needs thicker wire, a smaller mean diameter or more active coils — all of which increase size and cost.

What is the spring rate formula and how do I use it?
For a helical compression spring:
k=Gd48D3Nk = \frac{G d^4}{8 D^3 N}k = \frac{G d^4}{8 D^3 N}

where ( k ) = spring rate (N/mm) 
( G ) = shear modulus (≈80 000 MPa for carbon steel, ≈70 000 MPa for stainless) 
( d ) = wire diameter (mm) 
( D ) = mean coil diameter (mm) 
( N ) = number of active coils
Example: carbon-steel spring, d = 2 mm, D = 20 mm, N = 10 → k = 2.0 N/mm.
This is the theoretical value; always verify critical springs with a load-deflection test.What does “active coils” mean in spring calculations?
Active coils are the coils that actually deflect under load and contribute to the spring rate. In a closed-and-ground compression spring the end coils are inactive (“dead”). A spring with 12 total coils typically has about 10 active coils.
The rate formula uses active coils only. Using total coils produces an artificially high (stiffer) result. When measuring for replacement, count all visible body coils and then subtract the inactive end coils according to the end type.

What spring material is best for food-processing or pharmaceutical applications ?
316 stainless steel (ASTM A313 Type 316) is the standard choice. The molybdenum content gives superior resistance to chloride-based cleaners (sodium hypochlorite) and caustic soda. Request material test certificates confirming ASTM A313 compliance when formal certification is required. Passivated or electropolished finishes improve both cleanability and corrosion resistance. Confirm final suitability against current FSANZ requirements for the specific end use.

Can I order custom springs through AIMS?
Yes. AIMS works with Australian and overseas spring manufacturers and can source custom springs from a technical specification.
Provide free length, wire diameter, OD, end/hook type, material, finish and either rate or load-at-height for compression/extension springs. For torsion springs add body length, leg lengths, free angle and wind direction. A photograph of the original or broken spring is often the best starting point. Contact the AIMS team via the website or call (02) 9773 0122.

People Also Ask — Types of SpringsWhat are the main types of industrial springs?
The four primary types are compression (resist shortening), extension (resist stretching), torsion (store rotational energy) and flat springs (leaf and disc springs for axial loads). Compression springs are by far the most common.

What is a compression spring used for?
They resist compression and return to free length when the load is removed. Typical uses include valve returns, tooling fixtures, clutches and suspension systems. Key parameters are free length, loaded length, load at that height, coil diameter and wire diameter.What is spring rate, and why does it matter?
Spring rate (stiffness) is the force needed to deflect the spring one unit of length (N/mm). A high rate means a stiff spring; a low rate means a soft spring. Matching rate to the required force and travel is essential for correct performance.What materials are industrial springs made from?
Most are carbon or alloy spring steel (chrome-silicon or chrome-vanadium). 304 or 316 stainless is used for corrosion resistance (marine, food, chemical). Inconel and titanium are reserved for extreme temperature or aggressive chemical service.How do you select the right spring for an application?
Define the force required at the working height, free length, available space (OD/ID), expected cycles and operating environment. Spring suppliers use these inputs to select wire size, coil diameter and number of turns. For critical applications always supply a full specification rather than relying on a nearest catalogue size.