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When a project demands consistent spring force across a long stroke, undersized or mismatched springs cause premature failure, uneven load distribution, and costly rework. Engineers, hobbyists, and maintenance technicians who need a dependable black steel compression spring in a 305 mm (12 inch) length will find this range covers virtually every common wire diameter from 0.3 mm to 3 mm.
Each spring is wound from carbon steel wire with a black oxide or phosphate finish that provides a degree of surface protection against light moisture and handling wear. The body length is a consistent 305 mm (~12.0 in), with wire diameters spanning 0.3 mm (~0.012 in) to 3 mm (~0.118 in) and coil outer diameters ranging from approximately 3 mm to 40 mm depending on the selected variant. End types are closed and ground for flat seating.
Typical use cases include DIY mechanical assemblies requiring long-travel compression springs, custom jigs and fixtures where a specific wire-diameter-to-coil-diameter ratio is needed, and light industrial maintenance applications such as valve return springs, drawer slides, and tensioning mechanisms.
Wire diameters from 0.3 mm to 3 mm paired with coil outer diameters from 3 mm to 40 mm — all at a consistent 305 mm body length for long-stroke applications.
Flat-ground end coils ensure perpendicular seating, reducing lateral buckling and improving load accuracy in guided spring assemblies.
The dark surface treatment reduces bare-metal reflectivity, offers light corrosion inhibition during storage and handling, and suits applications where appearance matters.
Carbon steel wire delivers a good balance of tensile strength and elasticity for general-purpose compression duty across a wide range of loads.
A standardised 305 mm (~12 in) free length makes these springs easy to cut-to-length or use as-is in long-travel mechanisms, drawer systems, and custom fixtures.
Thinner wire (0.3–0.8 mm) suits light-duty return and tensioning tasks; heavier wire (1.5–3 mm) handles more substantial compression loads in mechanical assemblies.
| Material | Carbon steel |
|---|---|
| Finish | Black oxide / black phosphate |
| Body Length | 305 mm (~12.0 in) |
| Wire Diameter Range | 0.3 mm – 3 mm (0.012 in – 0.118 in) |
| Outer Diameter Range | See variant options |
| End Type | Closed and ground |
| Spring Direction | Right-hand wound |
| Spring Rate | See variant options |
| Max Load | See variant options |
| Operating Temperature | Up to approximately 120 °C (248 °F) for standard carbon steel |
| Corrosion Resistance | Light — suitable for dry/indoor environments |
Wire diameter determines the spring rate and maximum load capacity. Thinner wire (0.3–0.8 mm) produces softer springs suited to light return or tensioning tasks. Heavier wire (1.5–3 mm) creates stiffer springs for more substantial compression loads. Match the wire diameter to your required spring rate and the space available for the coil outer diameter.
For a housing (bore) fit, the spring outer diameter should be slightly smaller than the bore ID — typically 0.5–1 mm clearance. For a mandrel (rod) fit, the spring inner diameter should be slightly larger than the rod OD. Check the variant size label (wire Ø × coil OD × length) and calculate inner diameter as: OD − (2 × wire diameter).
Carbon steel compression springs in the 1.5–3 mm wire diameter range are well suited to general mechanical assemblies including valve returns, drawer mechanisms, and tensioning systems. For safety-critical or high-cycle fatigue applications, consult a mechanical engineer and verify the spring rate and load data for your specific variant.
The black oxide finish provides light surface protection against handling and short-term storage in dry conditions. These springs are not rated for wet, outdoor, or chemically aggressive environments. For corrosive conditions, consider stainless steel springs or apply an additional protective coating after installation.
Yes — the 305 mm body length is a common reason customers choose this range. You can cut carbon steel springs to a shorter free length using a rotary cutting tool or spring cutter. After cutting, the end coils will no longer be ground flat, so account for this in your design or dress the cut end as needed.
Spring rate (k) can be estimated using the formula: k = (G × d⁴) / (8 × D³ × n), where G is the shear modulus of carbon steel (~79,000 MPa), d is wire diameter, D is mean coil diameter (OD − d), and n is the number of active coils. If you need the exact spring rate for a variant, contact us with the size and we can provide further data.
The 0.3 mm wire diameter produces a very fine, soft spring ideal for delicate mechanisms such as small electronics, pen clips, or precision instruments. The 3 mm wire diameter produces a substantially stiffer spring capable of handling significant compressive loads in heavier mechanical assemblies. The 94 variants in between allow you to dial in the exact stiffness your project requires.
Each listing is sold per individual spring. If you need larger quantities for a project or production run, please contact us directly — we can discuss volume options and ensure you receive consistent batch specifications.
