A purchase order that says “green die spring” leaves a surprising amount undecided. Green identifies a load class only after the standard system is known. It does not tell you the exact force, the available travel or whether the spring fits the tool. For an ISO 10243 die spring, the color code is a useful starting point; the series drawing and load table complete the specification.
This guide explains the four core colors, separates manufacturer extensions from the standard range, and shows how to turn a color reference into a spring specification that an engineer and a buyer can both check.
Understand the boundary of ISO 10243
ISO 10243:2019 addresses rectangular-section compression springs for pressing tools, including housing dimensions and color coding. The official ISO scope excludes material and service life. A color reference therefore cannot establish either of those properties.
For procurement, separate three questions: does the spring match the specified standard and housing, does its documented force suit the mechanism, and does the supplier support the required operating conditions? An ISO reference helps organize the first question. The second and third still require the exact product data and an application review.
Rectangular-section die springs are used where substantial compressive force must fit inside a limited envelope. That does not mean every rectangular-wire spring belongs to the same standard or is interchangeable with another spring that looks similar.
Read the four core colors within the correct system
The core ISO 10243 identification sequence is green, blue, red and yellow. Catalogues may describe the last two classes as heavy/extra-heavy or strong/extra-strong. These naming differences should be reconciled with the stated standard and series, rather than treated as separate specifications.
| Colour | Core load class | What it helps identify | What still needs checking |
|---|---|---|---|
| Green | Light | A lighter class within the ISO range | Actual force and permissible deflection |
| Blue | Medium | The medium class within the same system | Force at both working heights |
| Red | Strong / heavy | A higher load class within the ISO range | Available travel for the selected series |
| Yellow | Extra strong / extra-heavy | The highest of these four core classes | Fit, working travel and application suitability |
The mapping is reflected in the manufacturer's Dayton MaxLife official color reference; use current product data for selection. The table above is an identification guide, not a force table. Two green springs with different sizes or free lengths need not deliver the same force.
Keep light-green and grey extensions separate
Some European-style catalogues add extra-light and very-high-load grades, including light-green or grey products. These are supplier-specific extensions, not two extra core ISO color classes. Their names, part codes and permitted deflections must come from the relevant catalogue.
For example, Special Springs identifies its extra-light VL series as a manufacturer-standard series. Other suppliers use different colors for expanded ranges. There is no reliable universal six-color ladder covering all of them.
When requesting an extended grade, include the manufacturer and full series code. Do not write only “grey ISO spring” on the order, and do not assume an extension shares the travel limit of the nearest core color. Ask for the drawing and the force-versus-deflection data for that exact part.
Confirm the housing before comparing load classes
A catalogue's hole diameter and rod diameter describe the intended housing arrangement. They are not automatically the measured outside and inside diameters of the coil. Check how the supplier defines each dimension and clearance.
- Confirm the bore diameter, guide-rod diameter and pocket depth from the tool drawing.
- Record the free length and the available axial space through the complete motion.
- Check the spring's actual dimensional limits against the bore and guide arrangement.
- Confirm square support surfaces, axial guidance and the specified installed height.
- Include manufacturing tolerances and assembly variation when checking the minimum working height.
A spring that fits when unloaded may still bind, rub or run out of axial space during operation. Use the series drawing together with the actual tool geometry. The die spring parameter guide is a useful way to organize the dimensions before narrowing the color choice.
Calculate preload and working travel explicitly
Define L0 as free length, Li as installed height at the beginning of the working motion, and Lw as minimum working height. For straight axial compression, using the same units:
- Preload deflection: L0 − Li.
- Additional working travel: Li − Lw.
- Maximum total deflection: L0 − Lw, equal to preload deflection plus additional working travel.
For an illustrative geometry with L0 = 100 mm, Li = 90 mm and Lw = 80 mm, the spring is precompressed by 10 mm and then moves another 10 mm. The maximum total deflection is 20 mm. These numbers explain the calculation; they are not a rating for a particular spring.
If deflection is expressed as a percentage of free length, use (L0 − Lw) ÷ L0 × 100%. Do not compare only machine stroke with a catalogue percentage: the machine motion may not equal the spring motion, and preload already uses part of the available deflection.
In a documented linear operating range, force can be estimated as F ≈ kδ, with k in N/mm and δ in mm. Use the manufacturer's force table or curve at Li and Lw, including its tolerance. A color name is not a numerical spring rate, and the force at maximum compression is not the force throughout the cycle.
Read travel, duty and material from the exact series
Higher load classes often provide more force over a smaller recommended travel range. Treat this as a selection tendency, not a universal percentage rule. Catalogues can distinguish recommended operating deflection, a longer-life setting, maximum operating deflection and solid deflection. These terms are not interchangeable.
Check which deflection includes preload, which operating conditions the recommendation assumes, and what evidence supports any stated life. Do not assign one fixed cycle count to all ISO springs. A supplier's catalogue-life figure is not automatically a guarantee in your press, where alignment, frequency and temperature may differ.
Specify material grade, temperature range and surface finish separately. ISO identification alone does not establish a universal 200 °C rating or a single alloy. Discuss corrosion, coating compatibility and operating temperature when reviewing surface treatment options; a coating choice does not replace the load and travel checks.
Compare ISO, JIS and US parts by data
The same paint color can represent a different class in another system. A JIS or US-series spring should therefore be compared with an ISO candidate by its complete part data, not by visual color matching. Also distinguish metric and inch dimensions before comparing sizes.
| Comparison item | Evidence to request | Decision it supports |
|---|---|---|
| Housing and length | Drawing, dimensional definitions and tolerances | Whether the spring can be installed correctly |
| Force | Force at specified installed and working heights | Whether the mechanism receives the required load |
| Travel | Permitted total deflection and solid-height information | Whether the complete motion stays inside the series limits |
| Operating conditions | Material, finish, temperature limits and stated duty assumptions | Whether the proposed part suits the application |
Even a matching ISO color and nominal housing size are not enough to approve a cross-supplier substitution. Confirm force, travel and documented limits. If the evidence differs, record the difference for engineering review rather than calling the parts equivalent.
Turn the color choice into a checkable RFQ
Attach the standard reference, full series or part number, bore and rod sizes, free length, Li and Lw, and the force required at each working point. State the number and arrangement of springs, operating frequency, environment and any acceptance or test requirement. Keep those requirements separate from the supplier's proposed catalogue rating.
Ask the supplier to return a drawing and a load table referenced to the same heights. Confirm the material and finish, and clarify whether an extended grade is a manufacturer-standard product. Understanding the spring winding process can help frame production questions, but process descriptions alone do not establish the performance of the ordered part.
Before approval, check that the quotation, drawing and purchase order use the same identifiers and units. The practical selection rule is straightforward: identify the color within its system, establish fit, then approve force and total travel from the exact series data.
Frequently asked questions
Does ISO 10243 have six core colors?
No. The four core classes are green, blue, red and yellow. Light-green, grey and other extended colors must be interpreted through the supplier's own series documentation.
Is yellow always the strongest spring?
Yellow identifies the extra-strong core ISO class, not the greatest force across every size and catalogue. Compare actual force at the required height; a larger spring in another class may deliver more force.
Can the same color establish interchangeability?
No. Confirm the standard, housing fit, dimensional tolerances, force at working heights, total deflection and operating conditions. This applies across standards and between suppliers using the same standard.
Does the catalogue travel limit include preload?
Check the definition in the exact catalogue. Calculate preload and additional working travel separately, then compare total deflection with the stated limit. Do not assume that a machine-stroke value represents all spring compression.
What should I send when the color or series is uncertain?
Send clear photographs, any part marking, the tool drawing, bore and rod dimensions, free length, installed and minimum working heights, and target forces. A photograph helps identify a candidate; it does not establish material, compliance or remaining life.
Discuss the specification with Dingli
Cixi Dili Spring Co., Ltd., founded in 1995, supports spring production from drawings or samples. If a catalogue color does not resolve your selection, send the installation dimensions and required working forces so Dingli Spring can review a suitable standard or custom specification.
Use the contact page, email jackchen@dinglispring.com, or WhatsApp +86 13586942004. Include the standard and full series reference when available, and identify any technical points that still require confirmation.
