3mm Spring Steel Black Compression Spring 16-27mm OD 20-200mm Length Rust Proof

Measure the bore or housing inner diameter your spring must fit inside — the spring OD should be 1–2mm smaller than the bore for clearance. Then measure the available travel distance and add it to your desired compressed length to determine the minimum free length you need. Select the variant whose OD and free length best match those measurements.

Load capacity depends on the specific OD, free length, and number of active coils of each variant. As a general guide, 3mm wire diameter springs in this OD range are suited to light-to-medium duty compression loads. For precise load and deflection data, contact us with your selected variant dimensions.

Black oxide provides good resistance to surface oxidation in moderately humid or indoor workshop environments. For prolonged outdoor exposure or immersion in water, we recommend applying a light coat of oil or grease to the spring surface as additional protection. The finish is not a substitute for stainless steel in fully corrosive environments.

These springs are designed with closed ends for stable seating on flat spring seats. Verify that your retainer or seat inner diameter is compatible with the selected OD variant. For custom retainer designs, the 3mm wire diameter and closed-end geometry are standard reference points for machining a matching seat.

These springs are suitable for light automotive sub-assemblies, jig fixtures, and general machinery where moderate cycle counts are expected. For safety-critical primary suspension or very high-cycle industrial automation, consult a mechanical engineer to verify the spring rate, fatigue life, and material specification match your design requirements.

The 2-piece pack is available for longer free-length variants (typically 150mm and 200mm) where per-unit cost is higher. The 5-piece pack is available for shorter to medium lengths and is the better choice when you need spares for maintenance or are building multiple assemblies. Select the QTY option that matches your project needs after choosing your size.

Wire diameter (3mm here) is the thickness of the steel wire used to coil the spring — it determines stiffness and load capacity. Outer diameter (OD, 16–27mm depending on variant) is the overall width of the coiled spring — it determines whether the spring fits inside a bore or over a guide rod. Both dimensions must be matched to your application for correct fit and function.