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When a ballpoint pen stops clicking, a sensor loses its return force, or a miniature mechanism fails to reset, the culprit is almost always a worn or undersized compression spring. DIY enthusiasts, electronics repair technicians, and model makers who need a reliable, dimensionally consistent replacement spring in small quantities will find exactly what they need here.
These small compression springs feature a wire diameter of 0.4mm and are available in outer diameters of 4mm, 4.3mm, and 4.5mm, with lengths ranging from 18mm to 30mm (approximately 0.71 in to 1.18 in). Two surface finishes are offered: Nature Colour (bare steel) and Zinc Coated for added corrosion resistance. Packs are available in 10, 20, 50, and 100 pieces to suit both one-off repairs and workshop stock.
Typical use cases include replacing worn ballpoint pen click springs, restoring spring-loaded latches in small electronics enclosures, and providing return force in miniature jigs, fixtures, and hobby mechanisms where a compact compression spring with consistent load characteristics is required.
Wire diameter 0.4mm; outer diameters 4mm, 4.3mm, and 4.5mm; free lengths 18mm, 20mm, 25mm, and 30mm — select the exact size your application demands.
Nature Colour (bare steel) suits dry indoor environments; Zinc Coated variants offer enhanced corrosion resistance for humid or outdoor-adjacent conditions.
Uniform wire diameter and coil pitch across the batch ensure repeatable load-deflection behaviour — critical for pen mechanisms and sensor return assemblies.
Available in 10, 20, 50, and 100-piece packs — order a small trial quantity or stock up for ongoing repair and prototyping work.
The slender 0.4mm wire and narrow OD allow these springs to fit inside tight bores and slim pen barrels where standard springs would not seat correctly.
Suited for ballpoint pens, click-action mechanisms, miniature latches, electronics enclosures, hobby models, and light-duty precision fixtures.
| Wire Diameter | 0.4mm |
|---|---|
| Outer Diameter | 4mm / 4.3mm / 4.5mm (see variant options) |
| Free Length | 18mm / 20mm / 25mm / 30mm (see variant options) |
| Material | Steel |
| Surface Finish | Nature Colour / Zinc Coated (see variant options) |
| Spring Type | Compression |
| Coil Direction | See variant options |
| End Type | Closed ends (typical for this wire gauge) |
| Pack Quantity | 10 / 20 / 50 / 100 pcs (see variant options) |
| Weight (per pack) | See variant options |
Measure the inner bore of your pen barrel and the existing spring's free length with a digital caliper. For most standard ballpoint pens, a 0.4mm wire diameter spring with a 4mm outer diameter and a free length of 20–25mm is the most common fit. If the bore is slightly larger, the 4.3mm or 4.5mm OD variants may seat more securely.
Nature Colour springs are bare steel with no surface treatment — suitable for dry indoor applications such as pen mechanisms and electronics enclosures where moisture exposure is minimal. Zinc Coated springs have a thin zinc layer that provides corrosion resistance, making them a better choice for environments with occasional humidity or where longer service life is needed.
Yes. At 0.4mm wire diameter these springs are designed for light-duty cyclic loading typical of pen click mechanisms and small latches. They maintain consistent return force over thousands of cycles under normal operating conditions. For heavy-duty or high-cycle industrial applications, a heavier wire gauge would be more appropriate.
For outdoor or humid conditions, select the Zinc Coated variant. The zinc layer significantly slows surface oxidation. Nature Colour springs are bare steel and will show surface rust if exposed to moisture over time, so they are best kept to dry indoor use.
For a single repair, a 10-piece pack gives you spares in case of installation errors. If you service pens or small electronics regularly, the 50-piece or 100-piece packs offer a lower per-unit cost and ensure you always have stock on hand. Match the OD and free length to your measured bore and required travel distance before ordering.
Yes. The 0.4mm wire / 4–4.5mm OD range suits any application requiring a compact compression spring with light return force — including miniature latches, sensor return mechanisms, hobby model assemblies, small jig fixtures, and electronic enclosure buttons. Check that your bore diameter and required free length fall within the available size options.
Inner diameter equals outer diameter minus twice the wire diameter. For the 4mm OD variant: ID ≈ 3.2mm. For 4.3mm OD: ID ≈ 3.5mm. For 4.5mm OD: ID ≈ 3.7mm. These are nominal values; contact us to confirm if your application has tight tolerance requirements.
