Complete Study Guide on Springs
Table of Contents
New to springs or just need a fast refresher? This study guide gives you quick, simple answers to the 37 most common questions beginners ask about compression, extension, and torsion springs. You’ll learn how springs work, how to measure and select the right one, how to estimate loads and rates with simple formulas, and where the practical limits are so you don’t over-stress a design. Whether you’re a student, a hobbyist, or an engineer working on your first spring-based mechanism, this guide keeps things approachable while pointing you to trusted references from The Spring Store and Acxess Spring, so you can move from questions to confident decisions, faster.
Springs work by storing and releasing mechanical energy through elastic deformation. When a force is applied, the spring’s shape changes (compresses, stretches, or twists) and energy is stored; when the force is removed, the spring returns to its original shape, releasing that stored energy. This allows springs to absorb shock, maintain force between components, and control motion in mechanical systems. Different spring types demonstrate this in various ways – for example, a compression spring shortens under load and pushes back when released, while a torsion spring twists and then returns with rotational force.
“Coil springs” usually refer to helical compression springs, and their job is to resist compressive force and push back to return to length. When you press on a coil spring, the coils squeeze together, storing energy; when you let go, the spring expands to push back with that stored energy. In practical terms, coil springs provide suspension, cushioning, and force in many applications. For example, in a car’s suspension a coil spring compresses over bumps to absorb shock and then expands to keep the tires in contact with the road. Coil springs can also simply maintain a force between two parts, like the spring under a battery contact or beneath a mechanical keyboard key.
Spring rate (also known as spring constant) is the measure of a spring’s stiffness , it tells you how much force is needed to compress or extend the spring by a certain amount. Technically, spring rate is expressed as force per unit of deflection (e.g. pounds per inch or newtons per millimeter). Knowing the spring rate is important because it lets you predict how much load causes how much deflection – it’s fundamental in spring design to ensure the spring will be strong enough yet flexible enough for the application.
Spring deflection, often just called spring travel, is the amount a spring moves under load. In other words, it’s the change in length (for compression/extension springs) or the angular rotation (for torsion springs) that occurs when the spring is subjected to a force. For a compression spring, deflection is how much shorter the spring gets when a load is applied; for an extension spring, it’s how much longer it gets when pulled; and for a torsion spring, it’s how many degrees it twists.
Springs are used everywhere in everyday life and engineering, anytime we need to store energy, absorb shock, apply a force, or return something to a position, a spring is likely doing the job. They appear in home appliances, vehicles, electronics, toys, machinery, the list is endless. For example, car suspension springs support the vehicle’s weight and smooth out bumps. Door hinges and screen doors use springs to close automatically. A ballpoint pen has a tiny coil spring that pushes the tip out and retracts it. Trampolines use many extension springs to give bounce. Even simple things like the clicker in a retractable pen or the spring in a clothes pin are springs at work. In short, springs are used to provide forces (push or pull), absorb energy (cushioning shocks or vibrations), and to return moving parts to a default position.
Manufacturing a spring involves forming springy metal wire into the coil shape and then heat treating it so it “remembers” that shape. For a coil spring (like a compression spring), the process typically starts with a spool of spring steel wire. This wire is fed into a coiling machine, often a CNC coiler, which winds the wire around a mandrel or arbor to form the helical coil of the desired diameter and pitch. The machine also forms any special end shapes (like hooks for extension springs or leg bends for torsion springs) as needed. After coiling, the spring is heat-treated (tempered) in an oven – this hardens the steel, so the spring can flex and return without taking a permanent set. Depending on design, additional steps can include grinding the ends flat (for compression springs to sit evenly), shot peening to improve fatigue life, and plating or coating to prevent corrosion.
Coil springs (helical springs) are made by taking spring steel wire and coiling it into a helix. In production, this is usually done with an automatic coiling machine that bends the wire around a rod to form the spring’s coils. The key factors in making a coil spring are the wire diameter, the coil diameter, and the number of coils, these are set on the coiling machine according to the spring’s design. Once coiled, the spring is removed from the coiling mandrel and then undergoes a heat treatment process. The heat treatment hardens the metal, which “sets” the coil shape, so the spring will have elasticity and return to shape after being compressed or stretched. For coil springs that need flat ends (common in compression springs), the ends may be ground flat after heat treat. If the coil spring is an extension spring (tension spring), the manufacturing is similar, except the coils are usually touching, and the machine will also create end loops or hooks from the wire.
Springs are typically made from spring steel wire, which is a high-strength, flexible metal wire formulated for elasticity. The most common spring wires fall into a few categories: high-carbon spring steel (like music wire ASTM A228), alloy steels (like chrome-silicon), and stainless steel for corrosion resistance. High-carbon music wire is very popular for its excellent tensile strength and cost-effectiveness, it’s what many coil springs are made of. Alloy spring wires (such as chrome-silicon or chrome-vanadium) are used for springs that see high stresses or elevated temperatures. Stainless steel wire (302/304 or 17-7 PH, for example) is used when springs need to resist rust or heat. But in all cases, the wire is round, metal, and capable of being hardened.
To design or replace a spring, you need to know more than just how it looks—you need the right numbers. Measuring and calculating spring properties is what makes it possible to match performance to your project’s needs.
Measuring a spring correctly means identifying several key dimensions. First, determine the spring type (compression, extension, or torsion) because each is measured a bit differently. For a compression spring, you’ll want to measure: (1) the wire diameter (thickness of the coil wire), (2) the outer diameter of the coil, (3) the free length, the overall length of the spring when it’s not compressed, and (4) the total number of coils. With those, you have the basic specs. In practice, using calipers to get wire and coil diameters, and a ruler for lengths, works well. By gathering these measurements, you fully characterize the spring’s size and can compare it to specifications or design requirements.
To measure a torsion spring, you need to capture a few specific dimensions unique to torsion springs. First, determine the wind direction of the spring, look at it: if the coils slope upward to the right, it’s right-hand wound; upward to the left is left-hand wound. Next, measure the wire diameter (the thickness of the spring wire). Then measure the outer diameter of the coil (or inner diameter, either one plus wire thickness, gives the other). Count the total number of coils in the spring. Finally, measure the length of each leg (the straight arms that stick out from the coil). So, a checklist for a torsion spring would be: wire diameter, coil outer diameter, total coil count, leg length 1, leg length 2, and wind direction. These measurements will let you identify or specify a torsion spring accurately. Also, note any bends or shapes in the legs (sometimes legs are not just straight but have bends – those matter too). By measuring all these aspects, you’ll have the complete picture of the torsion spring’s geometry needed for replacement or design.
When measuring an extension spring (tension spring), you’ll focus on both the coil and the hooks. Here’s how: measure the wire diameter first (the thickness of the spring’s coil wire). Then measure the outer diameter of the coils. Next, you need the body length, that’s the length of the coiled portion of the spring (from the beginning of the first coil to the end of the last coil, not including hooks). Also measure the length inside hooks, which is the overall length from the inner curve of one hook to the inner curve of the other hook (essentially the free length including the hooks minus the hook lengths). And note the hook type or shape (whether they are machine hooks, crossover hooks, side hooks, etc., or even if the spring has no hooks) since that can be important for how it attaches.
Measuring a coil spring (which usually means a compression spring) involves a few primary dimensions. You will want to measure the wire diameter (the thickness of the metal coil) and the outer diameter of the spring’s coils. Also measure the free length of the spring, this is the overall length of the spring when it’s completely unloaded (standing upright on a table, for instance). Another important count is the total number of coils the spring has. If the ends are flat (closed and ground ends), you might also note if any coils at the ends are inactive (pressed together), but generally counting total coils suffices. With compression springs, it can also be useful to note if the ends are ground flat or not, but as far as measuring, the four key parameters are: wire diameter, outer diameter, free length, and coil count. Using those measurements, you can compare the spring to catalogs or specifications to find a match or verify if it fits your needs.
To calculate a spring’s rate, you use a simple formula: spring rate = load / deflection. In practical terms, pick a certain amount of force (load) applied to the spring and measure how far the spring compresses or extends (deflection) under that load, then divide the force by the distance. The result is the spring rate (often denoted k). For example, say a compression spring is compressed 0.2 inches by a 5-pound weight. Dividing 5 lbs by 0.2 in gives a spring rate of 25 lbs/in. This means for each inch of compression, the spring would require 25 pounds of force.
If you have an existing spring, you can determine its rate by testing, for instance, apply a known weight and see how far the spring moves, then do force ÷ distance. On the other hand, if you are trying to figure out what spring rate you need for a design, you start from your required load and deflection: divide the desired load by the deflection to get the needed rate. For example, if you want a spring to compress 2 inches under a 20 lb load, you’d need roughly a 10 lb/in spring rate so that at 1 inch it resists with 10 lb. So, determine spring rate = needed force divided by allowed travel. Once you have that target rate, you would select or design a spring with that spring constant.
“Spring constant” is another term for spring rate, so finding it follows the same method: divide the force by the corresponding displacement. If you have a spring and want it constant, apply a known force and measure how much the spring moved. Note that spring constant is inherent to a spring’s design (material, coil dimensions, number of coils); you can’t change a given spring’s constant without modifying the spring itself, but you can compress it more or less (add preload) to change the force at a given point.
Replacing a recoil spring is generally straightforward with the right procedure. Ensure the device (firearm) is safe and unloaded first. Then you will disassemble the mechanism to access the recoil spring. In a semi-automatic pistol slide, for instance, this means removing the slide and taking out the recoil spring and its guide rod. The recoil spring is often under tension, so carefully compress it and ease it out (sometimes it’s a captive unit on a guide rod, sometimes not). Take the old spring off the guide rod or out of its channel, and then put the new recoil spring in place. Make sure to orient it correctly if it’s not symmetrical (some recoil springs have a tighter end coil that goes on a certain end, follow the manufacturer’s notes). After the new spring is seated, reassemble the mechanism (put the guide rod and spring back in, reattach the slide, etc.). Once reassembled, perform a quick function check, rack the slide or move the mechanism to ensure the spring is operating smoothly. In summary: unload, disassemble, swap the old recoil spring for new, reassemble, and that’s it. (Always refer to the specific firearm’s manual, as the disassembly steps can vary by model, but the concept of replacing the spring remains the same.)
Sometimes the best way to understand springs, or to get exactly what you need, is to build or customize one yourself. From simple DIY coils and tension springs to creating precise digital models in SolidWorks or Inventor, there are many ways to design a spring that fits your project.
In professional manufacturing, Acxess Spring uses CNC coiling machines to wind the spring and then an oven to heat treat it. Once that’s done, any finishing touches (like grinding flat ends or adding hooks) are made. The result is a spring that will compress or extend and bounce back. Note: Making quality springs can be tricky without the right equipment, controlling dimensions and heat treat is critical.
To make an extension spring (tension spring), the process is similar to making a compression spring with one key difference: extension springs have hooks or loops on the ends. Start with spring steel wire of the needed gauge. You’ll wind the wire into a coil with no gap between coils (extension springs are typically wound with the coils touching, to provide initial tension) around a mandrel of the desired diameter. Once the coil is formed to the right number of coils (length), you create the hooks. Commonly, you leave a bit of wire sticking out on each end and then bend those ends into loops. This can be done by gripping the end with pliers and forming a loop that comes around and touches the coil, creating the classic extension spring hook. Many extension springs use machine loops (loops that start from the end coil) or crossover loops, you’d choose the style based on strength needed. After coiling and looping, the spring is then heat-treated to impart the necessary springiness (harden the wire) if the wire isn’t already spring-tempered The result is an extension spring that will resist pulling forces. In summary: coil the wire tightly, form loops on the ends, and heat-treat, and you have a tension spring.
Small springs (miniature springs) are made with the same principles as larger springs, but they require precision and often specialized equipment due to their tiny size. Manufacturers that make very small springs use very fine spring wire, sometimes as small as a few thousandths of an inch in diameter (for example, wires on the order of 0.006″). The wire is coiled on high-precision machines or sometimes even by hand under microscopes for ultra-fine springs, around small mandrels. The coiling has to be very consistent because on a small spring even slight variations can throw off the spring’s behavior. After coiling, heat treatment is still needed for small springs to lock in the temper. Handling and cooling must be done carefully so as not to distort the delicate springs. Often, small spring manufacturers will use alloy steels or stainless steels that can handle the stress at small scales.
To make a spring “stronger” (meaning to increase its stiffness or the force it can exert), you have to change its design in ways that increase the spring rate or load capacity. There are a few classic ways: use a thicker wire, use a smaller coil diameter, or reduce the number of active coils. A thicker wire and/or a smaller coil makes the spring stiffer (imagine it’s harder to bend a thicker rod, or a tighter coil resists more). Likewise, fewer coils (shorter spring) means each coil bends less, making the spring stiffer. Another approach is using material with higher elastic modulus or tensile strength, though geometry changes usually have the biggest effect. It’s worth noting that making a spring much stronger increases stress in the material. So there’s a limit, if a spring is too stout (too high a rate) for its material and size, it might fail or take a set. But generally, to strengthen a spring’s action you modify dimensions: thicker, tighter, or shorter (or some combination of those).
Springs are designed to be elastic, meaning after you release a load they should return to normal. If your spring isn’t returning, it likely exceeded its elastic limit at some point. Once a spring has been permanently deformed (taken a permanent set), there is no simple way to “unstretch” or “uncompress” it back to factory specs. The best solution is usually to replace the spring. Ensuring a spring “goes back to normal” means using the right spring for the job (one that isn’t over-stressed) or giving it proper initial tension/preload so that it always comes back. If it’s damaged, though, no easy fix will fully bring it back, you’d need a new spring.
Making a spring “more powerful” can mean either increasing the force it outputs or the energy it stores. In general, to get more force from a spring, you’d design it similar to making it stronger/stiffer: use thicker wire, reduce coil diameter, or reduce coil count, all of which increase the spring rate and the force for a given deflection. If by “powerful” one means store more energy, you might increase its allowable deflection (a longer spring you can compress further) while maintaining a high force, but that gets into complex design trade-offs. Practically, if you have an existing spring and want it to be more powerful, you can sometimes preload it (compress it initially) so that it starts with more force. But that doesn’t change the spring’s rate, it just raises the baseline force. So truly, making a spring more powerful requires a stiffer spring design. Keep in mind, a much stiffer spring will require more force to compress at all, which might or might not be desirable. And a word of caution: more power (stiffness) means higher stress, so there’s a limit before the spring material can’t handle it.
Creating a spring-loaded mechanism involves integrating a spring such that it stores energy and provides a force or motion when needed. To design one, follow these steps conceptually: choose the type of spring that suits the motion, a compression spring if you need pushing force (or to return something to a position by pushing), an extension spring if you need pulling force (like a retracting action), or a torsion spring if you need a rotational push (twisting force). Then, design mounts or seats for the spring in your mechanism. The key is that in the “loaded” position, the spring is deflected (compressed, stretched, or twisted) and thus is storing energy. When you release whatever constraint, that energy will move the mechanism. So, to make your mechanism: incorporate a spring in a position where it will be deflected by the user or by some force, and upon release it will return the mechanism to a desired position or exert a force.
Choosing the right spring is about balancing fit, force, and function. Whether you’re selecting a general-purpose compression or extension spring, dialing in the right coilover spring rate for a vehicle, or figuring out which torsion spring best suits your mechanism, the process starts with knowing your requirements.
Selecting the right spring comes down to matching a spring’s type and specifications to the requirements of your project. Start by identifying the spring type needed (compression, extension or torsion). Next, gather key requirements: the space available (what diameter and length must the spring fit into), the force or torque needed at a certain deflection, and how much deflection (travel or angle) the spring needs to undergo. Also consider environmental factors (does it need to be stainless for corrosion? Does it face high temperatures?).
With those in hand, you can either go to a spring catalog or use an online spring finder tool.
Choosing the correct torsion spring for your needs involves a few key considerations. First, determine the torque you need the spring to provide and the angle of rotation through which it will be applied. This tells you the required spring rate in torsion (in inch-pounds per degree, for example) and how far the spring must twist. Next, consider the physical constraints: the space where the spring will fit, the maximum coil outside diameter allowed, the length (number of coils) that can fit, and the diameter of the shaft the spring will wind around (torsion springs are usually mounted on a shaft). You also need to know the leg configuration: how and where will the spring’s legs anchor to your mechanism? Torsion springs have two legs that exert force when rotated – you must pick a spring with leg lengths and orientation that suit your design (or plan to bend them to suit).
Determining which torsion spring you need is essentially about matching a spring to your specific application’s requirements. You’ll want to pin down a few details:
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Required torque: How much twisting force must the spring apply? For example, if it’s a torsion spring for a garage door, it must support the door’s weight via cables – that translates to a certain torque. For a small device, maybe you just need enough torque to flip a latch back. Knowing the torque (or at least the comparative strength needed) is step one.
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Angle of twist (travel): How many degrees will the spring be wound from its neutral position in use? Torsion springs can only twist so far safely. If your application rotates 90°, or 180°, it's important to select a spring that can handle that deflection.
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Dimensions: Measure the diameter of the shaft or rod the spring will go over (the spring’s inner diameter must be slightly larger than that). Measure any space constraints for the spring’s outer diameter. Also figure out how long the spring can be – this relates to the number of coils and wire size. The available space tells you maximum coil diameter and length.
- Leg configuration: How and where will the spring’s legs attach? Torsion springs have two legs (or ends) that need to be anchored. Common configurations are 90° apart, 180° apart, etc., depending on whether it’s a close-wound spring with legs at specific positions. You need a spring with legs oriented in a way that fits your mounting points, or one that you can bend the legs to suit.
Using these parameters, you “shop” for a spring. If you have an existing spring (say on a mousetrap or a clip) and you want a replacement, measuring that spring’s wire diameter, coil diameter, coil count, and leg lengths will directly tell you what you need. If it’s a new design, you may use a torsion spring design calculator by plugging in your desired torque at angle to get a starting wire size and coil count, then adjust to fit dimensions.
Figuring out the spring rate you need starts with your desired force and deflection. Ask: “How much force do I want the spring to exert, and over what distance will the spring move?” Spring rate is measured in force per distance (e.g. lb/in or N/mm), so essentially you divide the force by the deflection to get the rate.
If you’re replacing a spring and want the same behavior, you’d try to match the original spring’s rate. If you’re designing a new mechanism, calculate the rate. Keep in mind the spring’s physical limits: having the right rate is one thing, but the spring must also fit in the space and not coil-bind or yield at full load.
So the quick answer: you need a spring rate that produces your required force at your working deflection. Use the formula k = F/Δx. Many spring suppliers list spring rates for stock springs; you pick the one closest to what you calculated.
As a short answer: choose a coilover spring rate that supports the vehicle’s weight with the desired amount of suspension travel. If uncertain, use guidelines from similar builds or start with manufacturer’s recommendations, then adjust if needed. Remember, spring rate works with damping – you’ll also adjust the shock absorbers to match the chosen spring rate, so the combo works properly.
Even the best springs can lose tension, wear out, or simply stop performing the way they should. Knowing how to spot problems and apply quick fixes can save you time, money, and frustration.
If by “tighten” a spring you mean increase the force it’s exerting (often done by adding preload), the method depends on spring type.
To “tighten” a spring, you typically add preload: compress a compression spring further, stretch an extension spring a bit at rest, or pre-wind a torsion spring. This will increase the force at the start position.
Keep in mind, there’s a limit: over-preloading can cause a spring to bind (in compression) or to deform (in extension, you might take out all slack and then some). So you adjust until the spring is just tight enough.
To weaken a spring (make it softer or reduce the force it applies), you generally do the opposite of what you’d do to strengthen it. If it’s a design question, you’d choose a spring with a lower spring rate: for example, use a thinner wire, a larger coil diameter, or more active coils, these changes make a coil spring less stiff
If you need to stretch a spring (literally make it longer or increase its free length), be aware that once you stretch a spring beyond its elastic limit, it won’t fully spring back, you’ll have permanently deformed it. In general, stretching a coil spring by pulling it apart is not a recommended method to adjust a spring, because you’ll reduce its force and could compromise its integrity.
For an extension spring, the coils are initially touching (providing initial tension). If you physically pull the coils apart to make the spring longer, you’ll reduce or eliminate that initial tension. This will make the spring easier to stretch in use (because you removed the built-in preload). Sometimes people do this if a spring is too strong, they stretch it slightly so that it has less tension at rest. However, doing so also means the spring may not return fully, or the hooks may carry more load than intended.