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When a mechanical assembly demands consistent return force and fatigue resistance across repeated cycles, the wrong spring becomes a costly failure point. Engineers, fabricators, and serious DIY builders working on suspension systems, industrial machinery, or custom jigs need springs that hold their rated load without set or distortion. These black compression springs are designed for exactly that kind of demanding, load-critical work.
Each spring is formed from steel wire with a 6mm wire diameter and finished in a black surface treatment for corrosion inhibition. Outer diameters range from 28mm to 47mm (approximately 1.10" to 1.85"), and free lengths span 105mm to 190mm (approximately 4.13" to 7.48"), covering a broad range of cavity and travel requirements. Closed and ground ends provide flat, stable seating on both contact surfaces.
Typical use cases include automotive suspension bump stops, industrial press tooling, heavy-duty door return mechanisms, and custom CNC or 3D-printer Z-axis assemblies — all scenarios where a compression spring for machinery or a heavy-load return spring is specified by dimension rather than catalog number.
Thick-gauge wire construction delivers high spring rates suited to heavy-load compression applications in industrial and automotive assemblies.
Six outer diameter options (28–47mm) and four free-length options (105–190mm) let you match the spring precisely to your pocket or guide rod dimensions.
The black finish provides a baseline layer of corrosion inhibition, extending service life in moderately humid or oily environments compared to bare steel.
Flat, ground end coils ensure square seating against spring seats and retainers, reducing lateral deflection and improving load linearity under compression.
Steel construction maintains dimensional stability through repeated compression cycles, making these springs reliable for dynamic applications with frequent actuation.
Each variant ships as an individual spring, allowing you to order the exact quantity needed for prototyping, repair, or small-batch production without excess stock.
| Wire Diameter | 6mm (0.236") |
|---|---|
| Outer Diameter (OD) | 28mm / 30mm / 32mm / 34mm / 45mm / 47mm |
| Free Length | 105mm / 155mm / 160mm / 190mm |
| Material | Steel |
| Surface Finish | Black treatment |
| End Type | Closed & ground |
| Spring Rate | See variant options |
| Load Capacity | See variant options |
| Pack Quantity | 1 piece per pack |
| Inner Diameter (ID) | See variant options |
Measure the inner diameter of your spring pocket or the outer diameter of your guide rod. For a pocket-mounted spring, the OD should be 1–2mm smaller than the pocket bore to allow free movement. For a rod-guided spring, the ID (OD minus twice the wire diameter) should be 1–2mm larger than the rod diameter. Select the OD option that satisfies whichever constraint applies to your assembly.
Free length is the uncompressed length of the spring. You need enough free length so that, at maximum compression in your assembly, the spring does not reach solid height (coil bind). As a starting point, your working compressed length should be at least 20–30% shorter than the free length. Choose the free-length option that gives you adequate travel while fitting within your assembly's available space.
The 6mm wire diameter places these springs in the heavy-duty category for compression springs. They are suitable for automotive bump stops, industrial press tooling, and machinery return mechanisms. For safety-critical structural applications, always verify the spring rate and load capacity against your engineering requirements before installation.
The black surface treatment provides a protective layer that inhibits surface oxidation in moderately humid or oily environments. It is not equivalent to hot-dip galvanizing or stainless steel for fully outdoor or submerged applications. For high-moisture or chemically aggressive environments, consider applying a compatible grease or protective coating after installation.
Compression springs with a high length-to-diameter ratio can buckle under load if unsupported. For free lengths significantly greater than three times the outer diameter, a guide rod or pocket is strongly recommended to prevent lateral deflection. For shorter free lengths relative to OD, unsupported use may be acceptable depending on the load and alignment of your application.
Each variant is sold as a single piece (1 pcs per pack). This allows you to order the precise quantity needed — whether for a single repair, a prototype build, or a small production run — without committing to bulk quantities.
The 2mm difference in outer diameter affects which spring pocket or guide rod bore the spring will fit. If your assembly specifies a 45mm or 47mm bore, select the matching OD to maintain the recommended 1–2mm clearance. Both options share the same 6mm wire diameter and 190mm free length, so the spring rate and travel characteristics will be similar — the key differentiator is the fit within your housing.
