Medium load Compression Die Spring 6mm-50mm Diameter & Up To 500mm Long JIS

Measure the bore diameter of your spring pocket with a caliper. Select the outer diameter (OD) that is 0.1–0.5 mm smaller than the pocket bore to allow free movement without binding. For example, if your pocket bore is 12.3 mm, choose the 12 mm OD spring. Always verify the inner diameter clears your guide rod with at least 0.2 mm of radial clearance on each side.

JIS B 5012 classifies die springs by load color: light (blue), medium (green), heavy (red), and extra-heavy (yellow). Medium-load green springs offer a balanced spring rate — firmer than light-load springs for reliable stripping and ejection, but not so stiff that they require excessive press tonnage to compress. They are the most common choice for general-purpose stamping dies, injection mold ejector plates, and automation fixtures where moderate, consistent return force is needed.

Free length should equal your required working stroke plus the compressed length at maximum deflection. For medium-load springs, the recommended maximum deflection is typically 30–40% of the free length. For example, if your die stroke is 20 mm and you want to stay within 35% deflection, you need a free length of at least 20 ÷ 0.35 ≈ 57 mm — so you would select the next available length above that value. Always leave a safety margin to avoid coil bind.

These springs carry a corrosion-resistant protective surface finish suitable for typical workshop environments and intermittent coolant exposure. For continuous immersion in aggressive cutting fluids or high-humidity environments, we recommend wiping the springs dry after use and applying a light machine oil periodically to extend service life. If your application involves prolonged chemical exposure, contact us to confirm suitability.

Yes. Because these springs are manufactured to JIS B 5012 medium-load (green) dimensions, they are dimensionally interchangeable with other JIS-compliant green-class springs. Match the OD, ID, and free length of your worn spring to the corresponding variant in this listing. No re-machining of spring pockets or guide rods is required as long as the dimensions match.

Rectangular-section (flat) wire fills the coil cross-section more efficiently than round wire, allowing more active coils within the same free length and OD envelope. This results in a higher load capacity, lower solid height, and longer fatigue life at equivalent deflection percentages. Round-wire springs are generally lower cost but are not recommended for precision die and mold applications where consistent load and compact solid height matter.

Replace a die spring when you observe any of the following: visible cracking or fracture of coils, a measurable reduction in free length (more than 3–5% shorter than the original), inconsistent stripping or ejection force during production, or coil bind occurring before the intended stroke endpoint. Proactive replacement during scheduled die maintenance — rather than waiting for failure — prevents unplanned downtime and part defects.