{"product_id":"0-4mm-miniature-compression-spring-pen-refill","title":"Wire Diameter 0.4mm Miniature Ballpoint Pen Refill Compression Spring galvanised","description":"\u003cdiv class=\"hdiy-desc\"\u003e\n\u003cdiv class=\"hdiy-overview\"\u003e\n\u003ch2\u003e0.4mm Wire Diameter Miniature Compression Springs — Precision Fit for Pen Refills \u0026amp; Small Mechanisms\u003c\/h2\u003e\n\u003cp\u003eWhen a ballpoint pen stops clicking smoothly or a small mechanical assembly loses its return force, the culprit is almost always a worn or incorrectly sized compression spring. Engineers, repair technicians, and hands-on DIYers who work with miniature mechanisms know how frustrating it is to source a spring with the exact wire diameter, outer diameter, and free length needed — especially at the 0.4mm wire gauge scale.\u003c\/p\u003e\n\u003cp\u003eThese miniature compression springs feature a wire diameter of 0.4mm and are available in outer diameters of 4mm, 4.3mm, and 4.5mm (~0.157\"–0.177\"), with free lengths ranging from 18mm to 30mm (~0.71\"–1.18\"). The silver finish variants are bright steel; the galvanizing finish variants carry a zinc-coated surface for added corrosion resistance. Packing options run from 10 pieces up to 1,000 pieces per order.\u003c\/p\u003e\n\u003cp\u003eThese 0.4mm wire diameter compression springs are well suited for ballpoint pen refill replacement, precision instrument assembly, electronic device button mechanisms, and small appliance spring repair. Whether you are restocking a workshop drawer or sourcing components for a production run, the multi-quantity packing options make it straightforward to match your volume needs.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"hdiy-compat\"\u003e\n\u003cspan class=\"hdiy-compat-icon\"\u003e⚙️\u003c\/span\u003e \u003cstrong\u003eCompatibility:\u003c\/strong\u003e Designed to fit standard ballpoint pen refill housings and comparable miniature spring seats with an inner bore of approximately 3.2mm–4.1mm. Verify your housing bore and free-length clearance before ordering.\u003c\/div\u003e\n\u003cdiv class=\"hdiy-features\"\u003e\n\u003ch2\u003e✅ Key Features of These Miniature Compression Springs\u003c\/h2\u003e\n\u003cul class=\"hdiy-list\"\u003e\n\u003cli\u003e\n\u003cspan class=\"hdiy-icon\"\u003e📏\u003c\/span\u003e \u003cstrong\u003e0.4mm Wire Diameter:\u003c\/strong\u003e Consistent wire gauge across all size variants ensures predictable spring rate and reliable return force in tight-tolerance assemblies.\u003c\/li\u003e\n\u003cli\u003e\n\u003cspan class=\"hdiy-icon\"\u003e🔩\u003c\/span\u003e \u003cstrong\u003eMultiple OD \u0026amp; Length Options:\u003c\/strong\u003e Choose from OD 4mm, 4.3mm, or 4.5mm combined with free lengths of 18mm, 20mm, 25mm, or 30mm to match your exact application.\u003c\/li\u003e\n\u003cli\u003e\n\u003cspan class=\"hdiy-icon\"\u003e🛡️\u003c\/span\u003e \u003cstrong\u003eGalvanized or Silver Finish:\u003c\/strong\u003e The galvanizing option provides a zinc coating that resists surface oxidation in humid environments; the silver finish suits dry indoor mechanisms.\u003c\/li\u003e\n\u003cli\u003e\n\u003cspan class=\"hdiy-icon\"\u003e📦\u003c\/span\u003e \u003cstrong\u003eFlexible Pack Quantities:\u003c\/strong\u003e Available in packs of 10, 20, 50, or 1,000 pieces — order just enough for a repair job or stock up for ongoing production needs.\u003c\/li\u003e\n\u003cli\u003e\n\u003cspan class=\"hdiy-icon\"\u003e⚡\u003c\/span\u003e \u003cstrong\u003eConsistent Coil Pitch:\u003c\/strong\u003e Uniform open-coil winding maintains even load distribution along the spring body, reducing the risk of lateral buckling under compression.\u003c\/li\u003e\n\u003cli\u003e\n\u003cspan class=\"hdiy-icon\"\u003e🔄\u003c\/span\u003e \u003cstrong\u003eBroad Application Range:\u003c\/strong\u003e Beyond pen refills, these springs fit button-return mechanisms in electronics, sensor housings, small valve assemblies, and hobby model components.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"hdiy-table-wrap\"\u003e\n\u003ch2\u003e📐 Technical Specifications — Miniature Compression Springs\u003c\/h2\u003e\n\u003ctable\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003cth\u003eWire Diameter\u003c\/th\u003e\n\u003ctd\u003e0.4mm (~0.016\")\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003cth\u003eOuter Diameter (OD)\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\u003eFinish\u003c\/th\u003e\n\u003ctd\u003eSilver (bright) \/ Galvanizing (zinc-coated) — See variant options\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003cth\u003eSpring Type\u003c\/th\u003e\n\u003ctd\u003eOpen-coil compression\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 size range)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003cth\u003ePacking Quantity\u003c\/th\u003e\n\u003ctd\u003e10 \/ 20 \/ 50 \/ 1,000 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\u003cdiv class=\"hdiy-faq\"\u003e\n\u003ch2\u003e❓ Frequently Asked Questions\u003c\/h2\u003e\n\u003cdetails\u003e\n\u003csummary\u003eHow do I choose the right outer diameter for my pen refill?\u003c\/summary\u003e\n\u003cdiv class=\"hdiy-faq-body\"\u003e\n\u003cp\u003eMeasure the inner bore of your pen barrel or refill housing with a caliper. The spring OD should be slightly smaller than the bore — typically 0.2mm–0.4mm clearance — so it slides freely without binding. For most standard ballpoint refill housings, the 4mm OD variant is the most common fit; the 4.3mm and 4.5mm variants suit slightly wider housings.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n\u003csummary\u003eWhat is the difference between the Silver and Galvanizing finish?\u003c\/summary\u003e\n\u003cdiv class=\"hdiy-faq-body\"\u003e\n\u003cp\u003eThe silver finish is a bright steel surface with no additional coating, making it suitable for dry indoor environments where corrosion is not a concern. The galvanizing finish applies a zinc layer to the steel wire, which slows surface oxidation when the spring is exposed to moisture or humidity. For pen mechanisms used in normal indoor conditions, either finish performs reliably; choose galvanizing if the assembly may encounter condensation or damp storage.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n\u003csummary\u003eHow strong is a 0.4mm wire diameter compression spring?\u003c\/summary\u003e\n\u003cdiv class=\"hdiy-faq-body\"\u003e\n\u003cp\u003eAt 0.4mm wire diameter, these are light-duty springs intended for low-load applications such as pen click mechanisms, small button returns, and sensor contacts. The exact spring rate depends on the OD and free length of the specific variant. If your application requires a defined load value in Newtons or grams-force, contact us to confirm suitability before ordering.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n\u003csummary\u003eAre these springs compatible with non-pen applications?\u003c\/summary\u003e\n\u003cdiv class=\"hdiy-faq-body\"\u003e\n\u003cp\u003eYes. While the product title references ballpoint pen refills as a common use case, the dimensions make these springs suitable for any miniature mechanism that requires a light compression spring — including electronic button assemblies, hobby model suspensions, small valve returns, and precision instrument components. Verify the OD, free length, and wire diameter against your design tolerances before use.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n\u003csummary\u003eDo the springs resist corrosion over time?\u003c\/summary\u003e\n\u003cdiv class=\"hdiy-faq-body\"\u003e\n\u003cp\u003eThe galvanizing (zinc-coated) variants offer meaningful corrosion resistance for typical indoor and mildly humid environments. The silver (bright steel) variants are not coated and may develop surface oxidation if stored in damp conditions over extended periods. For long-term storage or use in environments with elevated humidity, the galvanizing finish is the recommended choice.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n\u003csummary\u003eCan I order a mixed selection of sizes in one order?\u003c\/summary\u003e\n\u003cdiv class=\"hdiy-faq-body\"\u003e\n\u003cp\u003eEach variant is sold as a separate line item defined by its WD × OD × Length combination, finish, and packing quantity. To receive multiple sizes, simply add each desired variant to your cart individually. The 10-piece packing option is ideal for sampling several sizes before committing to a larger quantity.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n\u003csummary\u003eWhat packing quantity should I choose for a production run?\u003c\/summary\u003e\n\u003cdiv class=\"hdiy-faq-body\"\u003e\n\u003cp\u003eFor prototyping or single repairs, the 10- or 20-piece packs keep costs low. For small-batch production or workshop restocking, the 50-piece pack offers a better per-unit value. The 1,000-piece pack is suited for ongoing production runs where consistent supply of a single size is needed. If you require quantities beyond 1,000 pieces, contact us to discuss your requirements.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/details\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"hdiy-cta\"\u003e🛒 Select your WD × OD × Length, Colour, and Packing Quantity above, then add to cart.\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cp\u003e \u003c\/p\u003e","brand":"HomeDIYer","offers":[{"title":"0.4*4*20mm \/ Silver \/ 10","offer_id":52450004992274,"sku":"GYWXWDLWJ00057x1","price":2.8,"currency_code":"USD","in_stock":true},{"title":"0.4*4*20mm \/ Galvanizing \/ 10","offer_id":52450005025042,"sku":"GYWXWDLWJ00058x1","price":2.9,"currency_code":"USD","in_stock":true},{"title":"0.4*4*25mm \/ Silver \/ 10","offer_id":52450005057810,"sku":"GYWXWDLWJ00059x1","price":2.8,"currency_code":"USD","in_stock":true},{"title":"0.4*4*25mm \/ Galvanizing \/ 10","offer_id":52450005090578,"sku":"GYWXWDLWJ00060x1","price":2.95,"currency_code":"USD","in_stock":true},{"title":"0.4*4*30mm \/ Silver \/ 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