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When a machine tool, stamping die, or injection mold relies on consistent return force, a worn or mismatched spring becomes the weakest link in the entire assembly. Engineers, toolmakers, and serious DIYers who need a dependable die spring in OD 6 mm or OD 8 mm will find this range covers the most common bore sizes — inner diameters of 3 mm (≈ 0.118 in), 4.1 mm (≈ 0.161 in), 4.3 mm (≈ 0.169 in), and 4.5 mm (≈ 0.177 in) — across three load ratings.
Each die spring is wound from rectangular-section alloy steel wire and finished with a color-coded powder coat that identifies its load class at a glance: Yellow = Light load, Blue = Medium load, Red = Heavy load, Green = Extra-heavy load, Brown = Ultra-heavy load. Outer diameters are 6 mm (≈ 0.236 in) and 8 mm (≈ 0.315 in); free lengths range from 10 mm (≈ 0.39 in) up to 300 mm (≈ 11.81 in). Packs contain 1 or 2 pieces depending on the selected variant.
Typical applications include punch-and-die sets for sheet-metal stamping, stripper plate springs in progressive dies, ejector pin return springs in plastic injection molds, and general-purpose compression spring replacement in jigs and fixtures where a standard round-wire spring lacks the load capacity or fatigue life needed for high-cycle production environments.
| Spring Type | Rectangular-wire die compression spring |
|---|---|
| Outer Diameter (OD) | 6 mm (≈ 0.236 in) / 8 mm (≈ 0.315 in) |
| Inner Diameter (ID) | 3 mm / 4.1 mm / 4.3 mm / 4.5 mm — See variant options |
| Free Length | 10 mm – 300 mm (≈ 0.39 in – 11.81 in) — See variant options |
| Load Class / Color | Light (Yellow) / Medium (Blue) / Heavy (Red) / Extra-Heavy (Green) / Ultra-Heavy (Brown) |
| Material | Alloy steel (rectangular cross-section wire) |
| Surface Treatment | Color-coded powder coat |
| Standard Reference | ISO 10243 / JIS B 5012 |
| Pack Quantity | 1 pc or 2 pcs — See variant options |
| Weight | See variant options |
Measure the guide pin diameter — your spring's ID should be 0.1–0.3 mm larger than the pin for a smooth sliding fit. Then measure the counterbore or pocket in your die plate; the spring OD should be 0.2–0.5 mm smaller than the pocket. For this range, OD 6 mm suits smaller precision dies while OD 8 mm is common in medium-duty stamping and molding tooling.
The color follows ISO 10243 / JIS B 5012 conventions: Yellow = Light load (lowest spring rate), Blue = Medium load, Red = Heavy load, Green = Extra-heavy load, Brown = Ultra-heavy load (highest spring rate). Match the color to your original spring or calculate the required spring force from your die design. When in doubt, start with the same color as the spring you are replacing.
The free length should be long enough so the spring is still under slight preload at the open (top-dead-center) position of the press, and short enough that it does not exceed roughly 30–35% deflection at full stroke. A common rule of thumb: free length ≈ stroke ÷ 0.30 for a starting point, then verify against the manufacturer's deflection chart for the specific load class.
Yes. Rectangular-section alloy steel die springs are specifically designed for repetitive-cycle tooling applications such as progressive stamping dies, blanking dies, and injection mold ejector systems. The rectangular wire cross-section stores more energy per unit volume than round wire, which extends fatigue life at equivalent deflection levels. Actual cycle life depends on the deflection percentage and load class selected.
The powder-coat finish provides basic corrosion resistance for indoor tooling environments with light coolant or cutting-fluid exposure. For prolonged outdoor use or immersion in water or aggressive chemicals, additional corrosion protection (such as periodic oiling or a stainless-steel alternative) is recommended. These springs are optimized for die and mold tooling rather than outdoor structural applications.
Pack quantity varies by variant — most shorter lengths (10 mm–95 mm) are sold in packs of 2, while longer lengths (100 mm and above) are typically sold as single pieces (pack of 1). The exact quantity is shown in the variant name under "Outer diameter x Length & Pack Quantity(Pcs)". Select the variant that matches your required length and the pack size will be displayed clearly.
Check three dimensions on your existing spring: outer diameter (OD), inner diameter (ID), and free length. Then match the color (load class). If all four parameters match, this spring is a drop-in replacement. If your existing spring has no color marking, measure the wire cross-section and compare the spring rate to the ISO 10243 table for the corresponding OD and load class.
