Compression Spring Wire Diamete 3.5mm,20-305mm Length Pressure Compressed Spring

Measure the bore or housing your spring sits inside (for an inside-fit spring) or the rod it slides over (for an outside-fit spring). For an inside-fit, the spring outer diameter should be 1–2mm smaller than the bore. For an outside-fit, the spring inner diameter (outer diameter minus twice the wire diameter) should be 1–2mm larger than the rod. Select the variant whose outer diameter matches your calculated target.

Free length is the uncompressed length of the spring. Measure the available cavity depth when the mechanism is fully open (unloaded). Your spring's free length should be equal to or slightly longer than this dimension so the spring is under a small preload when assembled. For precise applications, calculate the required deflection and spring rate to confirm the chosen length delivers the target load.

The material specification is listed on each individual variant. Typical options for springs in this wire diameter range include carbon steel (e.g., 65Mn) and alloy steel. If you require a specific material grade for corrosion resistance or temperature performance, please check the variant detail or contact us to confirm before ordering.

Standard carbon steel springs are not inherently corrosion-resistant. For outdoor, wet, or mildly corrosive environments, consider applying a protective coating after installation, or contact us to enquire about stainless steel or zinc-plated variants. For highly corrosive or marine environments, a stainless steel spring is strongly recommended.

Yes. These compression springs are commonly used in industrial machinery return mechanisms, valve assemblies, pneumatic and hydraulic systems, and automotive test fixtures. Always verify that the spring rate, load capacity, and dimensional specifications match your application's requirements before installation.

Spring rate (k) is calculated as: k = Gd⁴ / (8D³n), where G is the shear modulus of the material, d is the wire diameter, D is the mean coil diameter, and n is the number of active coils. If you know the required load (F) and deflection (x), then k = F / x. Use these values to select the variant whose spring rate most closely matches your requirement. Contact us if you need assistance with the calculation.

The quantity options refer to the number of identical springs included in a single order. The 1 pcs option is ideal for a single replacement. The 2 pcs option suits paired applications or provides a spare. The 5 pcs option is cost-effective for prototyping, small production runs, or stocking a workshop. All springs within a pack are the same size and specification.