{"product_id":"heli-coil-a3591-4cn250-thread-insert-1-4-28-unf-1d","title":"Heli-coil A3591-4CN250 Thread Insert 1\/4-28 Unf 1D","description":"\u003ch3\u003eProduct Description\u003c\/h3\u003e\n\u003cp\u003eThe HELI-COIL A3591-4CN250 is a screw-locking, tangless wire thread insert designed to restore or reinforce internal threads in parent materials that see sustained vibration or repeated fastener cycling. Manufactured from Grade 304 stainless steel with a bright finish, this insert installs into a prepared tapped hole and provides a hardened, corrosion-resistant thread form rated for up to 30 inch-pounds maximum locking torque. The tangless design eliminates tang removal after installation, reducing steps and the risk of debris in blind holes. At a 1D length-to-diameter ratio and 0.250 inches overall length, it suits applications where thread depth is limited.\u003c\/p\u003e\n\u003cp\u003eThis insert is used in metalworking, maintenance, and repair applications across industrial, aerospace, and mechanical service environments. Typical use cases include thread repair in aluminum, magnesium, or cast housings, and original equipment manufacturing where a hardened thread form is required in softer base materials. The 1\/4-28 UNF thread size fits fine-pitch fastener applications common in precision assemblies. Installation requires a properly sized HELI-COIL tap and compatible tangless installation tool. Sold individually.\u003c\/p\u003e\n\u003ch4\u003eKey Features\u003c\/h4\u003e\n\u003cul\u003e\n  \u003cli\u003eTangless design eliminates post-installation tang removal in blind or through holes\u003c\/li\u003e\n  \u003cli\u003eGrade 304 stainless steel construction resists corrosion in wet or chemically exposed environments\u003c\/li\u003e\n  \u003cli\u003eMaximum locking torque of 30 inch-pounds provides reliable thread locking under vibration\u003c\/li\u003e\n  \u003cli\u003eMinimum outside diameter of 0.306 inches and maximum of 0.326 inches for controlled fit in the tapped parent bore\u003c\/li\u003e\n  \u003cli\u003e5 free coils with a 1D length-to-diameter ratio suited to shallow thread engagement applications\u003c\/li\u003e\n  \u003cli\u003eBright finish with no coating additions that could affect dimensional tolerances\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch4\u003eCompatibility\u003c\/h4\u003e\n\u003cp\u003eDesigned as an OEM-style and repair thread insert for 1\/4-28 UNF tapped holes prepared with a HELI-COIL specification tap to match the 1D insert length series.\u003c\/p\u003e\n\u003ch4\u003eInstallation Notes\u003c\/h4\u003e\n\u003cp\u003eInstallation is performed by machinists or maintenance technicians using a HELI-COIL specification tap to prepare the parent bore, followed by a tangless insertion tool matched to the 1\/4-28 UNF insert series. Ensure the parent material is securely fixtured and the tapped hole is clean and free of chips or coolant before inserting. Do not use standard UNF taps in place of the required HELI-COIL oversized tap, as the insert will not seat correctly. Follow the manufacturer's installation tooling specifications for proper coil engagement depth.\u003c\/p\u003e\n\u003ch4\u003eTechnical Specifications\u003c\/h4\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003eThread Size\u003c\/strong\u003e: 1\/4-28 UNF\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eThread Standard\u003c\/strong\u003e: UNF\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eOverall Insert Length\u003c\/strong\u003e: 0.250 inches\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eLength to Diameter Ratio\u003c\/strong\u003e: 1D\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eNumber of Free Coils\u003c\/strong\u003e: 5\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eMinimum Outside Diameter\u003c\/strong\u003e: 0.306 inches\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eMaximum Outside Diameter\u003c\/strong\u003e: 0.326 inches\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eMaximum Locking Torque\u003c\/strong\u003e: 30 inch-pounds\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eMinimum Break Away Torque\u003c\/strong\u003e: 3.50 oz-in\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eMaterial\u003c\/strong\u003e: Stainless Steel\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eMaterial Grade\u003c\/strong\u003e: 304\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eCoating\/Finish\u003c\/strong\u003e: Bright\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eTang\u003c\/strong\u003e: Tangless\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eWeight\u003c\/strong\u003e: 0.001 pounds\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eNumber of Inserts\u003c\/strong\u003e: 1\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch4\u003eStandard Information\u003c\/h4\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003eBrand\u003c\/strong\u003e: HELI-COIL\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eManufacturer Part Number\u003c\/strong\u003e: A3591-4CN250\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"HELI-COIL","offers":[{"title":"Default Title","offer_id":51997250912562,"sku":"A3591-4CN250","price":22.54,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0270\/4519\/9983\/files\/d7742a14074e9e89ed74e608c2d1bf3e.jpg?v=1789993989","url":"https:\/\/voomisupply.com\/products\/heli-coil-a3591-4cn250-thread-insert-1-4-28-unf-1d","provider":"Voomi Supply","version":"1.0","type":"link"}