EUTypes of Springs and How to Choose Them
- Written By: Gavin Leo
- Updated By: CoCo
- Published:
- Updated
What do ballpoint pens, car suspensions and seat belt retractors have in common? They all operate using springs.
There are four common types of springs used in daily life: Compression Springs, Extension Springs, Torsion Springs and Constant Force Springs.
They store energy, absorb shocks, apply force, and control motion. In this guide, I’ll break down every major type of spring, what it does, and how to choose the right one for your application.
Different Types Of Springs
Compression Springs
Compression springs are the most common type of spring in the world. Their open-coil helical design creates space between each coil, allowing the spring to resist axial compressive force. When compressed, the coils close together and store energy; when released, they push back to their original length.
You’ll find them in everything from ballpoint pens and mattresses to engine valves and industrial machinery.
Extension Springs (Tension Springs)
Extension springs work in the opposite direction — they resist being pulled apart. The coils are wound tightly together at rest, creating built-in “initial tension” that must be overcome before the spring begins to extend. Hooks or loops at each end connect the spring to the components it pulls together.
Common applications include trampolines, garage door mechanisms, weighing scales, and retractable lids.
Torsion Springs
Unlike compression and extension springs, torsion springs store energy through rotation rather than linear movement. When a twisting force (torque) is applied, the spring resists and stores energy; release it, and it rotates back to its original position.
They come in helical form (used in hinges and clips) and spiral flat form (used in clocks and seatbelt retractors). Clothespins, mousetraps, and automatic door closers all rely on torsion springs.
Constant Force Springs
Constant force springs are unique in that they deliver a near-constant force throughout their entire stroke — regardless of how far they are extended. Made from tightly wound flat strips of spring steel, they resemble a roll of tape. As the strip is pulled out, the material’s inherent stress provides consistent resistance.
They are widely used in retractable seatbelts, tape measures, monitor height arms, and window blinds.
Leaf Springs
Leaf springs are made from multiple layers of rectangular metal plates — called “leaves” — stacked and clamped together to act as a single unit. Their robust structure makes them ideal for bearing heavy loads in vehicle suspension systems. The most common type is the semi-elliptical leaf spring, found in trucks, SUVs, and railway carriages.
They are valued for their simplicity, long service life, and low maintenance requirements.
Disc Springs (Belleville Washers)
Disc springs are conical-shaped metal washers designed to handle very high compressive loads within a minimal axial footprint. They can be stacked in series for greater deflection, or in parallel for increased load capacity.
This versatility makes them a go-to solution in clutch assemblies, bolted joints, aerospace actuators, and anywhere a large force must be maintained in a compact space.
Conical Springs
Conical springs are a variation of the compression spring, featuring a tapered helical coil with a diameter that gradually decreases from one end to the other. This design allows the larger coils to nest inside the smaller ones when fully compressed, resulting in an extremely low solid height.
They are inherently more laterally stable than cylindrical compression springs, making them well-suited for battery compartments, push-button mechanisms, and applications requiring variable spring rates.
Wave Springs
Wave springs are made from flat wire formed into a wave-like shape, rather than a traditional coil. This design delivers a useful load capacity in a significantly reduced axial space compared to conventional coil springs.
They are a popular choice in bearing preload applications, shaft seal assemblies, and any housing where axial space is tightly constrained.
Flat Springs
Flat springs are simple, stamped or bent metal strips that flex under load and return to their original shape when released.
Their low cost and compact form make them a practical solution for light-duty applications such as electrical contacts, snap-fit clips, locking latches, and consumer product mechanisms.
Garter Springs
Garter springs are formed by connecting the two ends of a coil spring into a continuous ring. This circular configuration allows the spring to exert a consistent, uniform radial force directed inward along its entire circumference.
They are primarily used as sealing elements — in oil seals, shaft seals, and pipe connectors — where maintaining constant contact pressure around a cylindrical surface is critical.
Open End Coil Springs
Open end coil springs, sometimes called tangential springs, continue on pitch all the way to the end of the spring without closing the final coil.
They are most frequently used when the spring needs to sit on a seat — common in automotive suspension applications. The advantage is that they do not require grinding, keeping production costs lower. The trade-off is that an open-end spring will not stand square on its own without a seat or other support.
Pigtail End Springs
Pigtail end springs feature a ground end coil that tapers down into a small, tight loop — resembling a pig’s tail. This design allows the spring to be bolted directly to a structure, enabling it to function under both compression and extension loads.
They are primarily used in vibrating conveyor systems, where the ability to handle bidirectional loading is essential.
Pigtail end springs feature a ground end coil that tapers down into a small, tight loop — resembling a pig’s tail. This design allows the spring to be bolted directly to a structure, enabling it to function under both compression and extension loads.
They are primarily used in vibrating conveyor systems, where the ability to handle bidirectional loading is essential.
How Springs Work: Hooke's Law Explained
Every spring — regardless of type — operates on one fundamental equation:
F = −kx
F
Restoring force exerted by the spring (Newtons or lbf)
K
Spring constant / spring rate (N/mm or lb/in)
x
Displacement from the spring’s natural rest position
The negative sign simply means the force opposes the displacement — push the spring in, it pushes back out.
What Is Spring Rate (k)?
Spring rate is a measure of stiffness. A spring with k = 10 N/mm requires 10 Newtons to compress it 1mm. High k = stiff. Low k = soft.
Four factors control spring rate:
- Wire diameter (d)：the most critical variable. Because d appears to the fourth power in the formula, a 2% change in wire diameter tolerance causes an ~8%shift in force output.
- Mean coil diameter (D)：larger diameter = softer spring
- Number of active coils (n)：more coils = softer spring, more travel
- Material shear modulus (G)：carbon steel G ≈ 11.5 × 10⁶ psi; stainless steel G ≈ 10 × 10⁶ psi — identical geometry springs in different materials will have different spring rates (Source: Century Spring)
The Elastic Limit
Hooke’s Law only holds within the spring’s elastic range. Exceed it, and the spring undergoes permanent plastic deformation — it will never return to its original shape. A spring over-compressed even once may never perform to spec again.
Linear vs. Variable Rate Springs
Most springs maintain a constant k throughout their travel — every millimeter of deflection requires the same force. These are called linear (constant rate) springs, and they’re the standard choice for most applications where consistent, predictable performance is required.
Variable (progressive) rate springs work differently — they get stiffer the more they compress. The conical spring is a classic example: wider coils bottom out first, leaving fewer active coils in play and progressively increasing the effective spring rate. This is why progressive rate springs are popular in automotive suspensions — soft enough for everyday comfort, stiff enough to resist bottoming out under heavy loads.
Common Spring Materials
Choosing the right material is just as important as choosing the right spring type. The material determines how your spring performs under load, how long it lasts, and whether it can survive its operating environment.
| Material category | Common grade | Key properties | Typical applications |
|---|---|---|---|
| Carbon steel | Music Wire (ASTM A228) | Highest tensile strength, excellent fatigue resistance, cost-effective | Precision instruments, compression & extension springs, general machinery |
| Alloy steel | Chrome-Silicon (ASTM A401) | High temperature resistance, exceptional resilience under heavy cyclic loads | Automotive suspension, engine valve springs, high-performance machinery |
| Stainless steel | 302 / 316 Stainless | Excellent corrosion and rust resistance; some grades are non-magnetic | Medical devices, food processing equipment, marine environments |
| Copper alloys | Phosphor Bronze | Superior electrical conductivity, corrosion resistant, non-magnetic | Electrical switches, conductive spring contacts, chemical industry |
| Nickel alloys | Inconel | Extreme heat resistance (up to 700°C+), strong acid and alkali corrosion resistance | Aerospace, gas turbines, nuclear power |
| Non-metals | Polyurethane / Composites | Lightweight, electrically insulating, oil-resistant, cushioning effect | Tooling industry, automotive bump stops, vibration damping |
How to Choose the Right Spring
This is the question I get asked most at Aria Manufacturing. And the honest answer is: it depends on five things. Work through each one in order, and the right spring will become obvious.
Step 1: Define the Load Type and Motion
- First, identify what the spring is actually doing:
- Being compressed axially? → Compression spring
- Being stretched/ pulling two parts together? → Extension spring
- Resisting a twisting or rotational force? → Torsion spring
- Needs to maintain constant forceregardless of deflection? → Constant force spring
- Supporting very high loads in a compact axial space? → Disc spring
- Part of a heavy vehicle suspension? → Leaf spring
Get this wrong, and nothing else matters.
Step 2: Determine Your Dimensions and Spring Rate
Once you know the spring type, pin down:
- Free length(unloaded) and working length (under load)
- Outside / inside diameter: must fit within your assembly envelope
- Required spring rate (k): use the formula: k = F ÷ x (force required divided by deflection)
If your application requires 100 N of force at 10 mm of compression, you need k = 10 N/mm. According to Century Spring’s selection guide, when free length is unknown, select a spring approximately 30% longer than the intended working length, then verify the load at working length matches your requirement.
For dynamic applications, only use the center 20–80% of the available deflection range to maintain linear behavior — the first and last 20% of travel are affected by end-coil contact effects.
Step 3: Assess Your Operating Environment
This is where most engineers drop the ball. Ask yourself:
- Temperature: above 120°C rules out music wire; above 250°C requires Inconel or equivalent
- Corrosion exposure: moisture, salt, or chemicals means stainless 316 or zinc plating with passivation
- Magnetic sensitivity: MRI and sensitive electronics require non-magnetic materials: phosphor bronze, stainless 316, or titanium
- Cleanliness requirements: medical and food applications require passivated stainless or titanium
- Cycle count: rarely cycled? Music wire is fine. Over 10,000 cycles? Specify fatigue-resistant alloy and consider shot peening
Step 4: Select Your Material
Match your environment to the right material:
- General purpose, dry, cost-sensitive→ Music wire (ASTM A228)
- Wet / outdoor / food contact→ Stainless 302 or 316
- High temperature or heavy cyclic loading→ Chrome-silicon or chrome-vanadium
- Electrical application→ Phosphor bronze
- Extreme heat or aerospace→ Inconel or titanium
- Medical implant / biocompatibility→ Titanium
Step 5: Specify Your Surface Treatment
Even after selecting the right material, don’t skip this step — especially for carbon steel springs:
- Indoor, general-purpose→ Zinc electroplating, clear passivation
- Outdoor or industrial→ Zinc electroplating, yellow passivation
- Medical / pharmaceutical / food→ Passivated stainless (no additional coating needed)
- High-cycle, fatigue-critical→ Shot peening (can be combined with plating)
- Color identification required→ Powder coating
- Low-reflectivity or aesthetic finish→ Black oxide + oil
The Spring Selection Guide By Industry
Springs are one of the few components that appear in virtually every industry. Here’s how different sectors rely on them:
| Industry | Applications | Spring types used |
|---|---|---|
| Automotive | Suspension system, engine valve control, clutch & brake, seatbelt retractor | Compression spring, leaf spring, disc spring, torsion spring, constant force spring |
| Electronics & Consumer | Keyboard switches, battery terminals, tape measures, earphone hinges, retractable pens | Compression spring, flat spring, constant force spring, torsion spring |
| Medical | Surgical instruments, auto-injectors, inhalers, orthopedic implants, catheter mechanisms | Compression spring, torsion spring, extension spring, titanium spring (stainless 316) |
| Industrial Machinery | Hydraulic valves, press tooling, overload couplings, vibrating conveyors | Compression spring (alloy steel), disc spring, pigtail end spring |
| Aerospace | Landing gear, engine fuel valves, actuation systems | Compression spring, disc spring, torsion spring, extension spring (Inconel / titanium) |
| Construction & Infrastructure | Heavy vehicle suspension, seismic vibration isolation, door and gate closers | Semi-elliptical leaf spring, large-diameter compression spring, torsion spring |
| Consumer & Home | Garage doors, trampolines, mattresses, mousetraps, window blinds | Torsion spring, extension spring, compression spring, constant force spring |
Frequently Asked Questions
Compression springs become shorter under load and push back. Extension springs become longer under load and pull back. Structurally, compression springs have open coils with visible gaps, while extension springs are tightly wound with coils touching at rest — giving them built-in initial tension from the first moment of loading.
Compression springs resist linear force along their axis — push them together, they push back. Torsion springs resist rotational force around their axis — twist them, they twist back. The spring inside a ballpoint pen is a compression spring; the spring inside a clothespin is a torsion spring.
Springs are most commonly made from carbon steel (music wire), stainless steel, alloy steel (chrome-silicon or chrome-vanadium), copper alloys (phosphor bronze), and nickel alloys (Inconel) for extreme environments. See the full material comparison table above for properties and typical applications.
Belleville washers, also called disc springs, are conical-shaped metal washers that resist very high compressive loads within a minimal axial space. They can be stacked in series for greater deflection or in parallel for greater load capacity.
Passenger cars use coil compression springs — either linear or progressive rate. Heavy trucks and commercial vehicles use semi-elliptical leaf springs for robust load-bearing. High-performance and motorsport vehicles use coilover setups that combine a compression spring with an adjustable shock absorber.
Springs are most commonly treated with zinc electroplating for corrosion protection, passivation for stainless steel in medical or food applications, powder coating for color-coding and UV resistance, shot peening for fatigue life in high-cycle applications, and black oxide for a decorative low-reflectivity finish.