A compression spring looks like the simplest part in the catalogue — a coil of wire that pushes back. But most compression springs that fail in service don't fail because the wire was wrong. They fail because of the ends, the proportions, or a buckling problem that a five-minute check would have caught.
This guide covers what actually decides whether a compression spring works: end types and when ground ends matter, how to spot a design that will be expensive or unstable before you send it out, how to choose material, and what to include in an RFQ. It's written for engineers and buyers specifying a custom spring — not picking one off a shelf.
Ask for a compression spring and you'll usually get a wire diameter, a coil diameter, a free length and a rate. What's missing is almost always the end treatment — and the ends decide whether the spring does its job.
| End type | What it is | When to use it |
|---|---|---|
| Closed and ground | End coils brought together, then ground flat | Precision work, load-line accuracy, springs that must stand square |
| Closed (squared) | End coils brought together, not ground | Cost-sensitive, lower-precision applications |
| Open | End coils left at pitch | Light-duty, special cases |
A compression spring transmits force along its axis. If the end isn't flat and perpendicular to that axis, the force doesn't act along the centreline — it acts at an angle. Three things follow:
Grinding the end coils flat fixes all three. The quality of that grind is measured as flatness — how close the ground surface is to a true plane, perpendicular to the spring axis. We grind to ≤ 0.01mm flatness for precision work.
Worth asking, because grinding adds cost and not every spring needs it.
You probably need them if:
You probably don't if:
Not sure? Tell your supplier what the spring seats against and how square it has to be, and let the end type follow from that. A good supplier will tell you when you're paying for a tolerance you don't need.
You don't need the full spring maths to catch the two problems that cause most surprises on a quote. Both take seconds.
Spring index = mean coil diameter ÷ wire diameter.
A spring at index 3 or 16 can usually still be made. It just costs more and scatters wider — better to know before you commit the design.
A compression spring too tall for its diameter will buckle — bow sideways instead of compressing straight — long before the wire is overstressed. It's a geometry problem, not a material one.
Slenderness = free length ÷ mean diameter.
If your design is tall and thin: guide the spring over a rod or in a bore, reduce the free length, or increase the diameter. Ground ends help too.
The most common material mistake is specifying by habit — copying the grade from the last drawing without asking whether the environment changed.
| Situation | Sensible choice |
|---|---|
| General industrial, dry, cost matters | Carbon / alloy spring steel — 65Mn, 50CrV, 55CrSi, 60Si2Mn. Excellent properties, low cost, but corrodes. |
| Moderate corrosion, general outdoor | Stainless 302 / 304 — the sensible default for most corrosion work |
| Chlorides, salt, more aggressive media | 316 — more molybdenum, better pitting resistance |
| Sustained high temperature | Specialty alloys. We run Inconel X-750 in production for high-temperature compression springs. |
| Severe chemistry, reagent contact | Super-austenitic grades. We sourced and processed 904L (1.4539) for a reagent-contact application where ordinary spring stainless wasn't enough. |
Two things worth knowing:
Tell your supplier the environment — temperature, media, expected life — rather than just a grade.
If a compression spring is failing in service, the symptom usually points at the cause.
| Symptom | Likely cause |
|---|---|
| Bows sideways under load | Slenderness too high — guide it, or change the proportions |
| Cracks starting on the inside of the coil | Stress concentrates on the inner face. Usually index too low, or overstressed for the cycle life |
| Load drops off over time (cold) | Set / relaxation — stressed too close to its limit |
| Load drops off at temperature | Wrong material for the operating temperature |
| Cocks in its bore | Ends not ground, or squareness not held |
| Pitting, then breakage | Corrosion — grade chosen for cost, not environment |
| Rate varies part to part | Index too high or too low, or tolerance stack |
The difference between a quote in a day and three rounds of emails:
No drawing? Send 3–5 samples. We analyse the material and performance and produce matched prototypes.
We're a custom compression spring manufacturer in Shanghai — IATF 16949 certified, 20+ years — making cylindrical, conical, barrel and tapered compression springs to drawing.
| Wire diameter | 0.1 – 20.0 mm |
| Spring types | Cylindrical / conical / barrel / tapered / custom |
| End types | Closed & ground (flatness ≤ 0.01mm), closed, open |
| Materials | Carbon/alloy (65Mn, 50CrV, 55CrSi, 60Si2Mn), stainless (301/302/304/316), specialty (X-750 in production, 904L on evaluation) |
| Prototypes | Matched samples within 7 days. $50 custom sample service, refundable. |
| Production MOQ | From 1,000 pcs for standard springs. Large springs and specialty materials quoted per piece — no minimum. |
| Quality | IATF 16949, full material traceability |
Ground ends to ≤ 0.01mm flatness are where we're genuinely strong. If your compression spring has to load square and sit true, that tolerance is the difference between a spring that works and one that cocks in its bore.
Send us your load, your working length and your bore — or just 3 samples. We'll tell you honestly what we can do.
Closed and ground, closed (squared), and open. Ground ends — flat to ≤ 0.01mm — for precision and load-line-critical work.
When the spring seats against a flat face or in a bore, when squareness is toleranced, when the mechanism is sensitive to side load, or when consistent solid height matters across a batch. If none of those apply, closed ends are usually enough and cost less.
To a flatness tolerance of ≤ 0.01mm.
Almost always because it's too tall for its diameter. If free length divided by mean diameter is much above 4, the spring will tend to bow sideways under load. Guide it over a rod or in a bore, shorten it, or increase the diameter. Unground ends make it worse.
Yes — cylindrical, conical, barrel, tapered and custom profiles to drawing.
Standard springs from 1,000 pcs. Large springs and specialty materials are quoted per piece — no minimum. Prototypes are always supported.
Yes. We run Inconel X-750 in production for high-temperature work and have processed 904L (1.4539) for a corrosion-critical application. Tell us the operating environment and we'll propose the grade.
Yes. Send 3–5 pieces; we analyse the material and performance and produce matched prototypes within 7 days.
±10% on load at a stated working height is routine. Tighter is possible, but should be discussed against the actual functional need — over-tolerancing is one of the biggest cost drivers in custom springs.
