{"product_id":"small-compression-springs-0-4mm-wire-dia-20-30mm","title":"Small Compression Springs Ballpoint Pen Spring 0.4mm Wire Dia 20 25 30mm Long","description":"\u003cdiv class=\"hdiy-desc\"\u003e\n\n  \u003ch2\u003eSmall Compression Springs for Ballpoint Pens \u0026amp; Precision DIY — 0.4mm Wire Diameter\u003c\/h2\u003e\n  \u003cdiv class=\"hdiy-overview\"\u003e\n    \u003cp\u003eWhen 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.\u003c\/p\u003e\n    \u003cp\u003eThese 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.\u003c\/p\u003e\n    \u003cp\u003eTypical 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.\u003c\/p\u003e\n  \u003c\/div\u003e\n\n  \u003cdiv class=\"hdiy-compat\"\u003e\n    \u003cspan class=\"hdiy-compat-icon\"\u003e🔧\u003c\/span\u003e\n    Compatible with ballpoint pens, small electronics assemblies, miniature latches, hobby models, and any application requiring a 0.4mm wire diameter compression spring with 4–4.5mm OD and 18–30mm free length.\n  \u003c\/div\u003e\n\n  \u003ch2\u003e✅ Key Features of These Small Compression Springs\u003c\/h2\u003e\n  \u003cdiv class=\"hdiy-features\"\u003e\n    \u003cdiv\u003e\n      \u003cspan class=\"hdiy-icon\"\u003e📏\u003c\/span\u003e\n      \u003cstrong\u003ePrecise Dimensional Range\u003c\/strong\u003e\n      \u003cp\u003eWire 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.\u003c\/p\u003e\n    \u003c\/div\u003e\n    \u003cdiv\u003e\n      \u003cspan class=\"hdiy-icon\"\u003e🛡️\u003c\/span\u003e\n      \u003cstrong\u003eTwo Surface Finish Options\u003c\/strong\u003e\n      \u003cp\u003eNature Colour (bare steel) suits dry indoor environments; Zinc Coated variants offer enhanced corrosion resistance for humid or outdoor-adjacent conditions.\u003c\/p\u003e\n    \u003c\/div\u003e\n    \u003cdiv\u003e\n      \u003cspan class=\"hdiy-icon\"\u003e⚙️\u003c\/span\u003e\n      \u003cstrong\u003eConsistent Spring Rate\u003c\/strong\u003e\n      \u003cp\u003eUniform wire diameter and coil pitch across the batch ensure repeatable load-deflection behaviour — critical for pen mechanisms and sensor return assemblies.\u003c\/p\u003e\n    \u003c\/div\u003e\n    \u003cdiv\u003e\n      \u003cspan class=\"hdiy-icon\"\u003e📦\u003c\/span\u003e\n      \u003cstrong\u003eFlexible Pack Quantities\u003c\/strong\u003e\n      \u003cp\u003eAvailable in 10, 20, 50, and 100-piece packs — order a small trial quantity or stock up for ongoing repair and prototyping work.\u003c\/p\u003e\n    \u003c\/div\u003e\n    \u003cdiv\u003e\n      \u003cspan class=\"hdiy-icon\"\u003e🔩\u003c\/span\u003e\n      \u003cstrong\u003eCompact Form Factor\u003c\/strong\u003e\n      \u003cp\u003eThe 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.\u003c\/p\u003e\n    \u003c\/div\u003e\n    \u003cdiv\u003e\n      \u003cspan class=\"hdiy-icon\"\u003e🔄\u003c\/span\u003e\n      \u003cstrong\u003eWide Application Compatibility\u003c\/strong\u003e\n      \u003cp\u003eSuited for ballpoint pens, click-action mechanisms, miniature latches, electronics enclosures, hobby models, and light-duty precision fixtures.\u003c\/p\u003e\n    \u003c\/div\u003e\n  \u003c\/div\u003e\n\n  \u003ch2\u003e📐 Technical Specifications — Compression Springs\u003c\/h2\u003e\n  \u003cdiv class=\"hdiy-table-wrap\"\u003e\n    \u003ctable\u003e\n      \u003ctbody\u003e\n        \u003ctr\u003e\n\u003cth\u003eWire Diameter\u003c\/th\u003e\n\u003ctd\u003e0.4mm\u003c\/td\u003e\n\u003c\/tr\u003e\n        \u003ctr\u003e\n\u003cth\u003eOuter Diameter\u003c\/th\u003e\n\u003ctd\u003e4mm \/ 4.3mm \/ 4.5mm (see variant options)\u003c\/td\u003e\n\u003c\/tr\u003e\n        \u003ctr\u003e\n\u003cth\u003eFree Length\u003c\/th\u003e\n\u003ctd\u003e18mm \/ 20mm \/ 25mm \/ 30mm (see variant options)\u003c\/td\u003e\n\u003c\/tr\u003e\n        \u003ctr\u003e\n\u003cth\u003eMaterial\u003c\/th\u003e\n\u003ctd\u003eSteel\u003c\/td\u003e\n\u003c\/tr\u003e\n        \u003ctr\u003e\n\u003cth\u003eSurface Finish\u003c\/th\u003e\n\u003ctd\u003eNature Colour \/ Zinc Coated (see variant options)\u003c\/td\u003e\n\u003c\/tr\u003e\n        \u003ctr\u003e\n\u003cth\u003eSpring Type\u003c\/th\u003e\n\u003ctd\u003eCompression\u003c\/td\u003e\n\u003c\/tr\u003e\n        \u003ctr\u003e\n\u003cth\u003eCoil Direction\u003c\/th\u003e\n\u003ctd\u003eSee variant options\u003c\/td\u003e\n\u003c\/tr\u003e\n        \u003ctr\u003e\n\u003cth\u003eEnd Type\u003c\/th\u003e\n\u003ctd\u003eClosed ends (typical for this wire gauge)\u003c\/td\u003e\n\u003c\/tr\u003e\n        \u003ctr\u003e\n\u003cth\u003ePack Quantity\u003c\/th\u003e\n\u003ctd\u003e10 \/ 20 \/ 50 \/ 100 pcs (see variant options)\u003c\/td\u003e\n\u003c\/tr\u003e\n        \u003ctr\u003e\n\u003cth\u003eWeight (per pack)\u003c\/th\u003e\n\u003ctd\u003eSee variant options\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003c\/tbody\u003e\n    \u003c\/table\u003e\n  \u003c\/div\u003e\n\n  \u003cdiv class=\"hdiy-faq\"\u003e\n    \u003ch2\u003e❓ Frequently Asked Questions\u003c\/h2\u003e\n\n    \u003cdetails\u003e\n      \u003csummary\u003eHow do I choose the right size compression spring for my ballpoint pen?\u003c\/summary\u003e\n      \u003cdiv class=\"hdiy-faq-body\"\u003e\u003cp\u003eMeasure 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.\u003c\/p\u003e\u003c\/div\u003e\n    \u003c\/details\u003e\n\n    \u003cdetails\u003e\n      \u003csummary\u003eWhat is the difference between Nature Colour and Zinc Coated?\u003c\/summary\u003e\n      \u003cdiv class=\"hdiy-faq-body\"\u003e\u003cp\u003eNature 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.\u003c\/p\u003e\u003c\/div\u003e\n    \u003c\/details\u003e\n\n    \u003cdetails\u003e\n      \u003csummary\u003eAre these springs strong enough for repeated click-action use?\u003c\/summary\u003e\n      \u003cdiv class=\"hdiy-faq-body\"\u003e\u003cp\u003eYes. 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.\u003c\/p\u003e\u003c\/div\u003e\n    \u003c\/details\u003e\n\n    \u003cdetails\u003e\n      \u003csummary\u003eCan I use these springs in outdoor or humid environments?\u003c\/summary\u003e\n      \u003cdiv class=\"hdiy-faq-body\"\u003e\u003cp\u003eFor 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.\u003c\/p\u003e\u003c\/div\u003e\n    \u003c\/details\u003e\n\n    \u003cdetails\u003e\n      \u003csummary\u003eWhich size and quantity combination should I order for a repair job?\u003c\/summary\u003e\n      \u003cdiv class=\"hdiy-faq-body\"\u003e\u003cp\u003eFor 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.\u003c\/p\u003e\u003c\/div\u003e\n    \u003c\/details\u003e\n\n    \u003cdetails\u003e\n      \u003csummary\u003eAre these springs compatible with mechanisms other than ballpoint pens?\u003c\/summary\u003e\n      \u003cdiv class=\"hdiy-faq-body\"\u003e\u003cp\u003eYes. 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.\u003c\/p\u003e\u003c\/div\u003e\n    \u003c\/details\u003e\n\n    \u003cdetails\u003e\n      \u003csummary\u003eWhat is the inner diameter of these springs?\u003c\/summary\u003e\n      \u003cdiv class=\"hdiy-faq-body\"\u003e\u003cp\u003eInner 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.\u003c\/p\u003e\u003c\/div\u003e\n    \u003c\/details\u003e\n\n  \u003c\/div\u003e\n\n  \u003cdiv class=\"hdiy-cta\"\u003e\n    🛒 Select your size, surface finish, and quantity above, then add to cart.\n  \u003c\/div\u003e\n\n\u003c\/div\u003e\n\n\u003cscript type=\"application\/ld+json\"\u003e\n{\n  \"@context\": \"https:\/\/schema.org\",\n  \"@type\": \"FAQPage\",\n  \"mainEntity\": [\n    {\n      \"@type\": \"Question\",\n      \"name\": \"How do I choose the right size compression spring for my ballpoint pen?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"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.\"\n      }\n    },\n    {\n      \"@type\": \"Question\",\n      \"name\": \"What is the difference between Nature Colour and Zinc Coated?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"Nature Colour springs are bare steel with no surface treatment — suitable for dry indoor applications. Zinc Coated springs have a thin zinc layer that provides corrosion resistance for environments with occasional humidity or where longer service life is needed.\"\n      }\n    },\n    {\n      \"@type\": \"Question\",\n      \"name\": \"Are these springs strong enough for repeated click-action use?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"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.\"\n      }\n    },\n    {\n      \"@type\": \"Question\",\n      \"name\": \"Can I use these springs in outdoor or humid environments?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"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.\"\n      }\n    },\n    {\n      \"@type\": \"Question\",\n      \"name\": \"Which size and quantity combination should I order for a repair job?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"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.\"\n      }\n    },\n    {\n      \"@type\": \"Question\",\n      \"name\": \"Are these springs compatible with mechanisms other than ballpoint pens?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"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.\"\n      }\n    },\n    {\n      \"@type\": \"Question\",\n      \"name\": \"What is the inner diameter of these springs?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"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.\"\n      }\n    }\n  ]\n}\n\u003c\/script\u003e","brand":"HomeDIYer","offers":[{"title":"0.4*4*20mm \/ 10pcs \/ Nature Colour","offer_id":52448862142738,"sku":"GLFBNHHDLWJ00057x1","price":3.06,"currency_code":"USD","in_stock":true},{"title":"0.4*4*20mm \/ 10pcs \/ Zinc Coated","offer_id":52448862175506,"sku":"GLFBNHHDLWJ00058x1","price":2.98,"currency_code":"USD","in_stock":true},{"title":"0.4*4*25mm \/ 10pcs \/ Nature Colour","offer_id":52448862208274,"sku":"GLFBNHHDLWJ00059x1","price":3.11,"currency_code":"USD","in_stock":true},{"title":"0.4*4*25mm \/ 10pcs \/ Zinc Coated","offer_id":52448862241042,"sku":"GLFBNHHDLWJ00060x1","price":3.2,"currency_code":"USD","in_stock":true},{"title":"0.4*4*30mm \/ 10pcs \/ Nature Colour","offer_id":52448862273810,"sku":"GLFBNHHDLWJ00061x1","price":3.33,"currency_code":"USD","in_stock":true},{"title":"0.4*4*30mm \/ 10pcs \/ Zinc 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