The four core ISO 10243 die spring colors are green for light load, blue for medium load, red for heavy load, and yellow for extra-heavy load. The color identifies a spring-rate class. To select or replace a spring, also check the housing dimensions, free length, force at the working height, and the supplier’s permitted deflection.
This guide provides the color chart, explains extended grades such as light green and grey, and shows which measurements to include in a purchase enquiry. Matching color alone does not establish interchangeability with a JIS or US die spring.
What ISO 10243 Actually Standardizes
ISO 10243:2019 covers rectangular-wire compression springs for pressing tools, including housing dimensions and color coding. Its four spring-rate classes are light, medium, strong, and extra strong.
The standard does not specify the spring material or its service life, and it does not define every dimension or guarantee product quality. For a purchase, use the standard together with the selected manufacturer’s drawing, load data, tolerances, operating limits, and inspection requirements.
Compare the available die spring ranges after confirming the intended standard and installation space.
The Four Core ISO 10243 Colors
At its heart, ISO 10243 defines four load classes. For any given bore and free length, the color tells you the relative stiffness: how much force the spring develops per millimeter of deflection.
| Color | Load class | Relative spring rate | Typical use |
|---|---|---|---|
| Green | Light load | Lowest of the four | Long-stroke, fatigue-sensitive jobs; pilots, strippers, sensors |
| Blue | Medium load | Moderate | General-purpose stamping, blank holders, balanced load/life |
| Red | Heavy load (strong) | High | Higher clamping force in the same bore; shorter stroke |
| Yellow | Extra-heavy load (extra-strong) | Highest of the four | Maximum force in a fixed pocket; short, hard-working strokes |
Within a comparable product family, a higher load class generally provides a higher rate and less available travel. Check the exact size and series: neither permitted stroke nor fatigue life can be calculated from coating color alone.
Where Light Green and Grey Fit: The Extended Grades
In real catalogs you will also see light green and grey die springs sold alongside the ISO four. These are extended grades that bracket the standard rather than additional official ISO colors:
- Light green — extra-light load. Sits below green. The softest rate with the longest permissible travel, for very fatigue-sensitive or long-stroke positions where even a light-load green spring would be too stiff.
- Grey — extra-extra-heavy load. Sits above yellow. The stiffest practical grade, for cases where a fixed bore must produce more force than even an extra-heavy yellow spring can deliver.
So a full, practical European-style range reads as a six-step ladder from softest to stiffest. At Dingli we identify these in the DL series as DLF (light green, extra-light) · DLL (green, light) · DLM (blue, medium) · DLH (red, heavy) · DLB (yellow, extra-heavy) · DLG (grey, extra-extra-heavy). The four middle grades follow the ISO 10243 color convention; the light green and grey ends extend the range so you can match a difficult pocket without changing the bore.
| Step | Color | Dingli DL code | Load class | ISO 10243 status |
|---|---|---|---|---|
| 1 (softest) | Light green | DLF | Extra-light | Extended grade |
| 2 | Green | DLL | Light | Core ISO color |
| 3 | Blue | DLM | Medium | Core ISO color |
| 4 | Red | DLH | Heavy | Core ISO color |
| 5 | Yellow | DLB | Extra-heavy | Core ISO color |
| 6 (stiffest) | Grey | DLG | Extra-extra-heavy | Extended grade |
The single most useful habit: never select on color alone. Color narrows the field; the published force-versus-deflection figure for that exact bore and free length is what you actually design to.
Load vs. Travel: Read the Exact Series Data
Use the data sheet for the exact spring size and series to distinguish maximum permitted deflection, recommended working deflection, and any tested fatigue conditions. These values are not interchangeable. A published cycle result applies to its stated minimum and maximum loads, speed, temperature, and test method.
Start with preload = free length − installed length. Add the extra working stroke to obtain maximum total deflection. Compare that total with the supplier’s operating limit, then check the force at both working heights.
Illustrative calculation: a 100 mm spring installed at 95 mm has 5 mm preload. A further 15 mm of motion produces 20 mm total deflection, or 20% of free length. This calculation describes the geometry only; it does not establish which color can meet the required load or cycle life.
For a linear rate k, the change in force over a working stroke is ΔF = k × Δs. Use the actual rate or measured curve for the selected part. Our spring stiffness guide explains how to calculate and compare working points.
Why ISO, JIS, and US Colors Are Not Interchangeable
This trips up a lot of cross-standard sourcing. The same color means a different load in each system, and the dimensions and travel ratings differ too. A red ISO spring is not a red JIS spring. Three reasons engineers must verify before substituting:
- Different bore and rod dimensions. ISO 10243 housings are not identical to JIS or US pockets, so a “matching” color may not even fit the hole and guide rod.
- Different load-per-color. Each standard assigns its colors to its own rate ladder. Matching color across standards does not match force.
- Different durability data. Compare each supplier’s stated test conditions and working limits. A standard name does not establish a universal cycle-life rating.
If you are weighing systems against each other, compare them deliberately rather than by color. Our breakdowns of JIS die springs and US die springs lay out where each fits, and we can cross-reference an existing part to the correct ISO equivalent on request — by recalculating load and travel, not by copying the color.
How to Select an ISO 10243 Die Spring
A reliable selection sequence for a European-standard die spring:
- Fix the pocket. Confirm the bore (hole) diameter and the guide-rod diameter. This sets the spring’s outside and inside diameter and rules out anything that will not fit.
- Set free length and installed height. The difference defines your preload; add the working stroke during the cycle to obtain total deflection.
- Define the force you need at the working point — not just at maximum compression.
- Pick the color/class whose force-versus-deflection curve delivers that force within its long-life travel window, not at its absolute limit.
- Check life. Compare the required force range and cycle target against the selected series’ working limits and validated test conditions.
- Confirm the environment. Specify operating temperature, corrosion exposure, and any special media. Confirm the material, finish, and permitted temperature for the exact product; ISO 10243 does not provide a universal material or temperature rating.
Surface condition, residual stress, heat treatment, and the operating environment can affect fatigue performance. Specify the finish and any inspection requirements for the application; see our surface treatment overview.
Common Mistakes With European Die Springs
- Selecting on color alone. Two springs of the same color but different free length deliver very different forces.
- Over-compressing a heavy color. Red, yellow, and grey have the smallest travel windows; treating them like a green spring causes set and early fracture.
- Assuming cross-standard color equivalence. ISO ≠ JIS ≠ US for the same color.
- Changing an intended matched set. Different rates change force sharing. Keep the specified set balanced unless the mechanism has been designed and checked for different rates.
- Ignoring preload. A spring installed with too little preload can surge or lift; too much wastes available stroke.
If your drawing specifies a color and a bore but you are unsure the travel and force actually match the duty, that is exactly the point to have it checked. A custom die spring built to your installed height and target force removes the guesswork when a catalog grade lands between two colors.
Frequently Asked Questions
Does ISO 10243 officially define six colors?
No. ISO 10243 standardizes four load classes — green (light), blue (medium), red (heavy), and yellow (extra-heavy). Light green (extra-light) and grey (extra-extra-heavy) are extended grades many manufacturers add to bracket the standard range, including our DLF and DLG grades.
Which color is the strongest?
Among the four ISO colors, yellow (extra-heavy) is the stiffest. If an extended grey/extra-extra-heavy grade is offered, it sits above yellow. Compare like sizes within the same series and verify the permitted working stroke in its data sheet.
Can I replace a JIS or American die spring with an ISO spring of the same color?
Not safely by color. The bore, rod, free length, load-per-color, and cycle basis all differ between standards. Match by recalculating fit, force, and travel for your installation — we can cross-reference a part for you.
How much can I compress an ISO die spring?
Use the permitted deflection for the exact series and size, including preload in the total. Check the working recommendation and fatigue-test conditions separately; color alone cannot establish a safe stroke or a cycle guarantee.
What material and temperature limit apply?
Confirm both on the supplier’s data sheet for the selected spring. Material, heat treatment, finish, stress, and duty all affect suitability; ISO 10243 does not itself assign a material or a universal temperature limit.
What information do you need to recommend the right spring?
Bore (hole) diameter, guide-rod diameter, free length, installed height, working stroke, target force at the working point, cycle expectation, and operating environment. With those, we can confirm the correct color and grade.
Work With Dingli
Choosing a European die spring is about matching force and travel to your pocket and duty cycle — the color is the shortcut, not the answer. If you are selecting a new ISO 10243 spring, cross-referencing an existing JIS or US part, or need a grade that falls between two colors, send us your bore, free length, installed height, and target load and we will confirm the right class or build a custom solution.
Talk to our engineering team via the contact page, email [email protected], or WhatsApp +86 13586942004. Founded in 1995, Cixi Dili Spring Co., Ltd. supports custom production from your sample or drawing across R&D, production, and sales.
