{"product_id":"4-40-countersunk-machine-screws","title":"4#40 Countersunk Machine Screws – Phillips or Hex Drive, Stainless or Carbon Steel (Nickel\/Black Zinc)","description":"\u003c!-- Part 1: Product Description HTML for Shopify --\u003e\n\u003cdiv class=\"hdiy-4-40-countersunk\"\u003e\n\u003c!-- Product Overview Section --\u003e\n\u003ch2\u003e🔩 4#40 Countersunk Machine Screws – Choose Phillips or Hex Drive, Stainless or Carbon Steel, Nickel\/Black Zinc\/Natural\u003c\/h2\u003e\n\u003cp\u003eYou’re working on a small electronic device, repairing a piece of furniture, or assembling a model – and you need a #4‑40 screw that sits flush. These countersunk machine screws are available with either a Phillips cross drive or a hex socket (Allen) drive, so you can pick the tool you prefer. Choose from 304 stainless steel for corrosion resistance or carbon steel (C1018) with nickel or black zinc plating. The flat 82° head sinks flush into a pre‑drilled countersink, leaving a smooth surface. Fully threaded, with overall length measured including the head. Available in lengths 5\/16″, 3\/8″, 0.4″, and 0.47″. Perfect for electronics enclosures, machinery, furniture, and DIY where a flush finish and reliable fastening are needed.\u003c\/p\u003e\n\u003c!-- Features Section --\u003e\n\u003ch2\u003e✨ Key Features – 4#40 Countersunk Machine Screws\u003c\/h2\u003e\n\u003cul class=\"hdiy-feature-list\"\u003e\n\u003cli\u003e🔽 \u003cstrong\u003eCountersunk flat head (82°)\u003c\/strong\u003e – Sits flush with the surface after proper countersinking. Smooth, snag‑free finish.\u003c\/li\u003e\n\u003cli\u003e💪\u003cbr\u003e\u003cstrong\u003eTwo drive options\u003c\/strong\u003e – Choose Phillips (cross recess) or Hex socket (Allen) to suit your tool preference.\u003c\/li\u003e\n\u003cli\u003e🛡️ \u003cstrong\u003eMaterial choices\u003c\/strong\u003e – 304 stainless steel (natural, corrosion‑resistant) or carbon steel C1018 with nickel or black zinc plating.\u003c\/li\u003e\n\u003cli\u003e📏 \u003cstrong\u003e#4‑40 UNC thread\u003c\/strong\u003e – Standard US coarse thread size (4 gauge, 40 threads per inch). Widely used in electronics and small assemblies.\u003c\/li\u003e\n\u003cli\u003e📐 \u003cstrong\u003eOverall length includes head\u003c\/strong\u003e – Example: 4#40 x 5\/16″ means total length from top of head to tip is 5\/16″. Fully threaded.\u003c\/li\u003e\n\u003cli\u003e💪 \u003cstrong\u003eStrong \u0026amp; durable\u003c\/strong\u003e – Good mechanical properties, wear resistance, and corrosion protection (depending on material\/plating).\u003c\/li\u003e\n\u003cli\u003e🏭 \u003cstrong\u003eWidely used\u003c\/strong\u003e – Furniture manufacturing, machinery assembly, electronic equipment, automotive, aerospace, medical devices, and shipbuilding.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c!-- Specifications Table --\u003e\n\u003ch2\u003e📏 Available Sizes – 4#40 Countersunk Screws (Overall Length)\u003c\/h2\u003e\n\u003cdiv style=\"overflow-x: auto;\" class=\"hdiy-table-wrapper\"\u003e\n\u003ctable class=\"hdiy-specs-table\"\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth\u003eThread Size\u003c\/th\u003e\n\u003cth\u003eOverall Length (inches, including head)\u003c\/th\u003e\n\u003cth\u003eHead Diameter (approx.)\u003c\/th\u003e\n\u003cth\u003eDrive Options\u003c\/th\u003e\n\u003cth\u003eMaterial \u0026amp; Finish Options\u003c\/th\u003e\n\u003c\/tr\u003e\n\u003c\/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd style=\"background: #f5f5f5; text-align: center;\" colspan=\"5\"\u003e📐 Length = from top of head to tip. Fully threaded. Select exact size, drive, material and finish from dropdown.\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr class=\"hdiy-table-row\"\u003e\n\u003ctd class=\"dia\"\u003e4#40\u003c\/td\u003e\n\u003ctd class=\"len\"\u003e5\/16\" (0.3125\")\u003c\/td\u003e\n\u003ctd rowspan=\"5\"\u003e0.18″ or 0.23″ (varies by length – see dropdown)\u003c\/td\u003e\n\u003ctd rowspan=\"5\"\u003ePhillips or Hex socket (Allen)\u003c\/td\u003e\n\u003ctd rowspan=\"5\"\u003e304 Stainless (natural) \/ Carbon steel (nickel plated or black zinc)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr class=\"hdiy-table-row\"\u003e\n\u003ctd class=\"dia\"\u003e4#40\u003c\/td\u003e\n\u003ctd class=\"len\"\u003e3\/8\" (0.375\")\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr class=\"hdiy-table-row\"\u003e\n\u003ctd class=\"dia\"\u003e4#40\u003c\/td\u003e\n\u003ctd class=\"len\"\u003e0.4\" (approx. 13\/32\")\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr class=\"hdiy-table-row\"\u003e\n\u003ctd class=\"dia\"\u003e4#40\u003c\/td\u003e\n\u003ctd class=\"len\"\u003e0.47\" (approx. 15\/32\")\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003cp style=\"font-size: 0.85rem; margin-top: 0.5rem;\" class=\"hdiy-note\"\u003e* Please allow minor tolerances (±0.002‑0.005″). Head diameter varies with length – refer to product dropdown for exact specifications.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c!-- Material \u0026 Drive Selection Guide --\u003e\n\u003ch2\u003e📋 How to Choose the Right Option\u003c\/h2\u003e\n\u003cdiv style=\"overflow-x: auto;\" class=\"hdiy-table-wrapper\"\u003e\n\u003ctable class=\"hdiy-specs-table\"\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth\u003eMaterial \/ Finish\u003c\/th\u003e\n\u003cth\u003eCorrosion Resistance\u003c\/th\u003e\n\u003cth\u003eBest For\u003c\/th\u003e\n\u003c\/tr\u003e\n\u003c\/thead\u003e\n\u003ctbody\u003e\n\u003ctr class=\"hdiy-table-row\"\u003e\n\u003ctd class=\"pro\"\u003e304 Stainless (natural)\u003c\/td\u003e\n\u003ctd class=\"desc\"\u003eExcellent – indoor\/outdoor, humidity, light marine\u003c\/td\u003e\n\u003ctd class=\"desc\"\u003eOutdoor furniture, marine electronics, medical devices\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr class=\"hdiy-table-row\"\u003e\n\u003ctd class=\"pro\"\u003eCarbon steel + nickel plated\u003c\/td\u003e\n\u003ctd class=\"desc\"\u003eGood – indoor use, light moisture\u003c\/td\u003e\n\u003ctd class=\"desc\"\u003eElectronics, appliances, visible fasteners\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr class=\"hdiy-table-row\"\u003e\n\u003ctd class=\"pro\"\u003eCarbon steel + black zinc\u003c\/td\u003e\n\u003ctd class=\"desc\"\u003eModerate – indoor, low‑glare finish\u003c\/td\u003e\n\u003ctd class=\"desc\"\u003eIndustrial equipment, dark assemblies\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003cp style=\"font-size: 0.85rem; margin-top: 0.5rem;\" class=\"hdiy-note\"\u003eDrive type: Phillips works with common crosshead screwdrivers; Hex socket (Allen) allows higher torque with matching hex key.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c!-- FAQ Section – all expanded --\u003e\n\u003ch2\u003e❓ Frequently Asked Questions – 4#40 Countersunk Screws\u003c\/h2\u003e\n\u003cdiv class=\"hdiy-faq\"\u003e\n\u003cdiv class=\"hdiy-faq-item\"\u003e\n\u003cp class=\"hdiy-faq-question\"\u003e\u003cstrong\u003e1. How do I measure the length of a countersunk screw?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp class=\"hdiy-faq-answer\"\u003eFor countersunk screws, length is measured overall – from the top of the head to the tip. So a “4#40 x 3\/8″” screw has a total length of 3\/8″ including the head.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"hdiy-faq-item\"\u003e\n\u003cp class=\"hdiy-faq-question\"\u003e\u003cstrong\u003e2. Do I need to countersink the hole?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp class=\"hdiy-faq-answer\"\u003eYes – these are true 82° countersunk screws (UNC standard). Drill a matching 82° countersink hole for a flush finish. Use a countersink bit slightly larger than the head diameter.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"hdiy-faq-item\"\u003e\n\u003cp class=\"hdiy-faq-question\"\u003e\u003cstrong\u003e3. Are these screws fully threaded?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp class=\"hdiy-faq-answer\"\u003eYes – all 4#40 screws in this range are fully threaded from under the head to the tip, giving you maximum grip in thin materials or when using nuts.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"hdiy-faq-item\"\u003e\n\u003cp class=\"hdiy-faq-question\"\u003e\u003cstrong\u003e4. What tool do I need for hex drive versions?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp class=\"hdiy-faq-answer\"\u003eHex socket (Allen) drive screws require a 0.050″ or 1\/16″ hex key (exact size varies – check product specs). Phillips versions use a #0 or #1 Phillips screwdriver.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"hdiy-faq-item\"\u003e\n\u003cp class=\"hdiy-faq-question\"\u003e\u003cstrong\u003e5. Will carbon steel screws rust outdoors?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp class=\"hdiy-faq-answer\"\u003eNickel or black zinc plating provides moderate protection for indoor and light outdoor use. For continuous outdoor or marine environments, choose 304 stainless steel.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"hdiy-faq-item\"\u003e\n\u003cp class=\"hdiy-faq-question\"\u003e\u003cstrong\u003e6. Can I use these screws with a nut? What size nut fits?\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp class=\"hdiy-faq-answer\"\u003eYes – these are machine screws. Use a standard #4‑40 UNC hex nut. They will also thread into pre‑tapped #4‑40 holes.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cstyle\u003e\n  .hdiy-4-40-countersunk {\n    max-width: 100%;\n    margin: 0;\n    padding: 0;\n    color: #1a1a1a;\n    line-height: 1.5;\n  }\n  .hdiy-4-40-countersunk h2 {\n    font-size: 1.75rem;\n    margin: 1.5rem 0 0.75rem 0;\n    font-weight: 600;\n    border-bottom: 2px solid #eaeaea;\n    padding-bottom: 0.5rem;\n  }\n  .hdiy-4-40-countersunk h2:first-of-type {\n    margin-top: 0;\n  }\n  .hdiy-4-40-countersunk p {\n    margin-bottom: 1rem;\n    font-size: 1rem;\n  }\n  .hdiy-feature-list {\n    list-style: none;\n    padding-left: 0;\n    margin: 1rem 0;\n  }\n  .hdiy-feature-list li {\n    margin-bottom: 0.75rem;\n    padding-left: 0.25rem;\n    font-size: 1rem;\n    display: flex;\n    align-items: flex-start;\n    gap: 0.5rem;\n  }\n  .hdiy-feature-list li strong {\n    font-weight: 600;\n  }\n  .hdiy-table-wrapper {\n    margin: 1.25rem 0;\n   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