Compression Spring Steel With Black Treatment 3~6mm Wire Dia & 305~400mm Length

Start with the bore or spring seat in your assembly. The outer diameter of the spring must fit freely inside the bore with a small clearance (typically 1–2 mm on each side). Then select a wire diameter that delivers the load and deflection you need — thicker wire produces a stiffer spring with higher load capacity. If you are unsure, measure your existing spring or consult a spring rate calculator using the outer diameter, wire diameter, and number of active coils.

Load capacity depends on the specific wire diameter, outer diameter, free length, and number of active coils of each variant. Carbon steel compression springs in the 2.3–6 mm wire diameter range typically handle light to medium loads suitable for jigs, fixtures, and general machinery. For precise spring rate and maximum load data, contact us with your selected variant dimensions and we can provide further guidance.

Black oxide is a conversion coating that provides mild corrosion resistance by reducing the rate of surface oxidation. It performs well in dry indoor environments. For outdoor use, high-humidity conditions, or exposure to chemicals, consider applying a light coat of oil or grease after installation to extend service life. If your application requires stronger corrosion protection, look for stainless steel or zinc-plated spring options.

Yes, carbon steel compression springs can be cut to a shorter free length using an angle grinder or spring cutter. After cutting, grind the end coil flat to restore a proper bearing surface. Keep in mind that cutting changes the number of active coils, which alters the spring rate — a shorter spring from the same wire and OD will be stiffer. Plan your cut length carefully based on your required travel and preload.

Yes. These springs are designed with standard coil geometry and can be used with inner mandrels (guide rods) or outer guide bores. For inner mandrel use, the mandrel diameter should be slightly smaller than the spring's inner diameter (outer diameter minus twice the wire diameter) to allow free compression without binding. Check the inner diameter of your selected variant before specifying a mandrel size.

Choose the free length that matches or slightly exceeds your required installed length plus maximum compression travel. The 305 mm variants are well-suited for compact assemblies and shorter stroke applications, while the 400 mm variants provide more travel range or allow you to cut down to a custom length. Both length families share overlapping wire and outer diameter options, so you can match the same cross-section in either length.

For initial prototyping or fit-checking, the single-piece (QTY 1) option lets you validate the spring dimensions and performance in your assembly before committing to more stock. Once confirmed, the 2-piece or 5-piece options offer a lower per-unit cost and ensure you have spares on hand for maintenance or batch builds. Select your quantity in the QTY(PCS) option above alongside your chosen size.