0.4mm Wire Dia Compression Spring 3/4mm OD 5-305mm Length A2 Stainless Steel

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0.4mm Wire Dia Compression Spring 3/4mm OD 5-305mm Length A2 Stainless Steel

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Wire Dia x Outer Dia x Length: 0.4x3x5mm

Pack Size(Pcs): 10

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$9.83 USD

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In stock (500 units), ready to be shipped

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0.4mm Wire Dia Compression Spring — Precision A2 Stainless Steel, 3–4mm OD, 5–305mm Length

When a project demands repeatable, consistent spring force in a compact envelope, undersized or mismatched springs cause premature fatigue, erratic return force, and costly rework. Engineers, hobbyists, and small-batch manufacturers who work with miniature mechanisms, precision instruments, or light-duty actuators need a reliable source of accurately dimensioned compression springs in corrosion-resistant material — available in the exact quantity they need.

These compression springs feature a 0.4 mm wire diameter and are available in two outer diameter groups: 3 mm (≈ 0.118 in) and 4 mm (≈ 0.157 in). Body lengths span from 5 mm (≈ 0.197 in) up to 305 mm (≈ 12.0 in), covering a wide range of travel requirements. Material is A2 stainless steel (equivalent to 304 / 18-8), cold-coiled with closed and ground ends on shorter lengths and open ends on longer rod-stock lengths. Pack sizes range from 1 to 200 pieces to suit prototyping through small-production runs.

Typical use cases include miniature electronics enclosures requiring tactile button return, precision optical and laboratory instrument assemblies needing consistent preload, and light-duty valve or latch mechanisms in food-processing or marine environments where corrosion resistance is essential. The 0.4 mm wire diameter compression spring in A2 stainless steel is also widely used in pen mechanisms, small relay contacts, and micro-switch actuators.

⚙️ Compatibility: Suitable for guide rods or bores sized to match the selected OD variant. 3 mm OD springs fit bores of approximately 3.1–3.5 mm; 4 mm OD springs fit bores of approximately 4.1–4.5 mm. Confirm free length and spring rate against your application load requirements before ordering.

✅ Key Features of These 0.4mm Wire Dia Compression Springs

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A2 Stainless Steel Construction

Cold-coiled from A2 (304) stainless steel wire, offering solid corrosion resistance in humid, wet, and mildly acidic environments without surface coating.

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Precise 0.4 mm Wire Diameter

Consistent wire gauge across the full range ensures predictable spring rate and deflection behavior, critical for repeatable force in miniature mechanisms.

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Wide Length Selection: 5–305 mm

From compact 5 mm (0.197 in) button-return springs to 305 mm (12.0 in) rod-stock lengths, a single product family covers diverse travel and preload requirements.

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Two OD Options: 3 mm and 4 mm

Choose 3 mm OD (≈ 0.118 in) for tighter bore fits or 4 mm OD (≈ 0.157 in) for slightly larger guide channels — both sharing the same 0.4 mm wire diameter.

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Flexible Pack Quantities

Order as few as 1 piece for prototyping or up to 200 pieces for small-batch production, minimizing excess inventory while keeping per-unit cost efficient.

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Fatigue-Resistant Cold Coiling

Cold-coiling process work-hardens the wire, improving fatigue life under cyclic loading compared to annealed alternatives — important for high-cycle switch and valve applications.

📐 Technical Specifications — Compression Spring

Wire Diameter	0.4 mm (0.016 in)
Outer Diameter	3 mm (0.118 in) or 4 mm (0.157 in) — see variant options
Inner Diameter	2.2 mm (3 mm OD) / 3.2 mm (4 mm OD) — approximate
Free Length	5 mm – 305 mm (0.197 in – 12.0 in) — see variant options
Material	A2 Stainless Steel (304 / 18-8)
Coil Direction	Right-hand
End Type	Closed (short lengths) / Open (rod-stock lengths) — see variant options
Spring Rate	See variant options
Surface Finish	Natural (uncoated stainless)
Pack Size	1 / 5 / 10 / 20 / 30 / 50 / 100 / 150 / 200 pcs — see variant options
Operating Temperature	Typically –20°C to +150°C (–4°F to +302°F)

❓ Frequently Asked Questions

How do I choose between the 3 mm OD and 4 mm OD variants?

Select based on your guide bore or rod diameter. The 3 mm OD spring fits bores of approximately 3.1–3.5 mm; the 4 mm OD spring fits bores of approximately 4.1–4.5 mm. Both share the same 0.4 mm wire diameter, so the spring rate will differ slightly due to the different mean coil diameter. If you are working on a rod guide, choose an OD that gives 0.1–0.3 mm clearance to the bore wall.

What free length should I order for my application?

The free length should be longer than your required compressed length plus the desired preload travel. As a general rule, select a free length that is at least 20–30% longer than the maximum compressed position to avoid coil bind. For example, if your mechanism compresses the spring to 10 mm, a free length of 13–15 mm is a reasonable starting point.

How strong are these springs — what load can they handle?

With a 0.4 mm wire diameter, these are light-duty miniature springs. Typical load capacity at full deflection ranges from a few grams-force (short, small-OD variants) up to several hundred grams-force (longer, larger-OD variants). Exact spring rate depends on the number of active coils, which varies by length. For precise load data, contact us with your specific size and deflection requirements.

Are A2 stainless steel springs suitable for outdoor or marine use?

A2 (304) stainless steel offers good corrosion resistance in most atmospheric and freshwater environments. It performs well in humid, wet, and mildly saline conditions. For prolonged immersion in seawater or exposure to chloride-rich environments, A4 (316) stainless steel is generally recommended. These springs are well-suited for indoor humid environments, food-contact equipment, and light outdoor applications.

Are these springs compatible with my existing guide rod or bore?

Yes, provided you match the OD to your bore size. The 3 mm OD variant works with guide rods up to approximately 2.0–2.2 mm diameter (inner diameter ≈ 2.2 mm). The 4 mm OD variant works with guide rods up to approximately 3.0–3.2 mm diameter. Always verify the inner diameter against your rod to ensure the spring slides freely without binding.

How do I decide how many pieces to order?

For prototyping or testing, a pack of 1–10 pieces is usually sufficient to validate fit and function. For small-batch production runs, packs of 50–200 pieces reduce per-unit cost and minimize reorder frequency. Consider ordering a slightly larger quantity than your immediate need to account for setup losses and future maintenance replacements.

Can these springs be used in high-cycle applications such as switches or relays?

Yes. Cold-coiled stainless steel springs have improved fatigue resistance compared to annealed wire springs. For high-cycle applications (millions of cycles), ensure the spring is not compressed beyond 80% of its free length during operation to stay within the elastic range and maximize service life. If your cycle count exceeds 10 million, contact us to discuss material and design options.

🛒 Select your Wire Dia x OD x Length and Pack Size above, then add to cart.