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When a mechanism fails to return, a door refuses to close, or a valve loses its snap, the culprit is almost always an undersized or worn-out compression spring. Engineers, hobbyists, and maintenance technicians who need a dependable, dimensionally consistent black compression spring with a 3mm wire diameter will find this listing covers an unusually wide selection of outer diameters and free lengths in a single place.
Each spring is wound from carbon steel wire with a black surface finish (typically phosphate-coated or black-oxide treated) that provides a degree of corrosion inhibition for indoor and light-duty environments. Wire diameter is 3mm throughout the range. Outer diameter (OD) options span 16mm to 40mm (~0.63" to 1.57"), and free lengths run from 20mm to 200mm (~0.79" to 7.87"). Packs of 2 or 5 pieces are available depending on the variant selected.
Typical use cases include: DIY furniture and cabinet hardware requiring consistent push-back force; light industrial machinery such as jigs, fixtures, and press tooling that need a 3mm wire compression spring for return actuation; and hobbyist robotics or 3D-printer bed-leveling assemblies where a compact, black-finish spring keeps aesthetics clean. Long-travel variants (150mm–200mm free length) suit suspension mockups and prototype shock-absorber testing.
| Wire Diameter | 3mm (0.118") |
|---|---|
| Outer Diameter (OD) | 16mm – 40mm (0.63" – 1.57") — See variant options |
| Free Length | 20mm – 200mm (0.79" – 7.87") — See variant options |
| Pack Quantity | 2 Pcs or 5 Pcs — See variant options |
| Material | Carbon steel |
| Surface Finish | Black (phosphate-style coating) |
| End Type | Closed and ground |
| Spring Type | Compression |
| Spring Rate | See variant options / Contact us to confirm |
| Max Load Capacity | See variant options / Contact us to confirm |
| Operating Temperature | Typically –20°C to +120°C (indoor/light-duty use) |
Measure the bore or guide rod your spring will sit in or around. The spring OD should be slightly smaller than the bore (typically 0.5–1mm clearance) or slightly larger than the guide rod (0.5–1mm). For free length, select a spring that is 20–30% longer than your required compressed length to ensure adequate preload and travel without coil bind.
Load capacity depends on the specific OD, free length, and number of active coils — all of which vary by variant. As a conservative estimate, 3mm wire carbon steel compression springs in this size range typically handle light-to-medium loads (a few Newtons to tens of Newtons depending on geometry). Contact us with your required spring rate or load at a specific deflection for a more precise match.
The black phosphate-style finish provides light corrosion resistance suitable for dry indoor and sheltered environments. For prolonged outdoor exposure, high-humidity, or submerged applications, we recommend applying a compatible grease or considering stainless steel springs instead. These springs are not rated for marine or chemical environments.
The springs themselves are identical — only the quantity per order differs. The 5-piece packs are available for smaller OD variants (16mm–27mm) and shorter-to-medium lengths, while 2-piece packs cover the larger OD and longer-length variants. Select the pack size that matches your project quantity to avoid over-ordering.
Yes. The 3mm wire diameter provides a stiffer return force than the thin 0.5–1mm wire springs commonly used in bed-leveling kits, making these better suited for heavier print beds or robotic joints that require more resistance. Choose a shorter free length (20–40mm) and a smaller OD (16–20mm) for compact mounting points.
Spring rate is not listed per variant because it varies with OD, free length, and active coil count. If you have a specific load requirement (e.g., "I need 15N at 30mm deflection"), please contact us via the store's message function with your OD, free length, and target load. We can advise on the closest matching variant or suggest an alternative.
Yes. All variants in this listing feature closed and ground ends, which provide a flat seating surface for stable load transfer and reduce the risk of lateral buckling during compression. This end type is standard for general-purpose compression springs used in machinery, fixtures, and consumer hardware.
