{
 "version": "2026-10-20",
 "license": "Dimension sheets are written by Xem Studio from the cited sources and are free to use (CC BY 4.0, attribute 'Xem Studio'). Linked files belong to their publishers under the license shown; Xem Studio does not host them. 'license_verified: false' means the license shown is from memory or the publisher's page as last read and should be confirmed at the link before commercial use.",
 "slug": "imperial-machine-screws",
 "name": "Imperial machine screws: #4-40, #6-32, #8-32, 1/4-20",
 "kind": "hardware",
 "category": "Hardware",
 "group": "Fasteners",
 "year": null,
 "question": "What are the clearance and tap drill sizes for #4-40, #6-32, #8-32 and 1/4-20?",
 "tags": [
  "screw",
  "fastener",
  "bolt",
  "imperial"
 ],
 "aliases": [
  "4-40",
  "6-32",
  "8-32",
  "1/4-20",
  "quarter twenty",
  "sae screw"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": false,
 "free_files": 18,
 "url": "https://xemstudio.com/objects/imperial-machine-screws/",
 "sheet_txt": "https://xemstudio.com/objects/imperial-machine-screws/sheet.txt",
 "sheet": {
  "basis": "ASME B18.6.3 / B18.3; Unified thread standard",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "Major diameters: #4 2.845 mm (0.112 in), #6 3.505 mm (0.138 in), #8 4.166 mm (0.164 in), 1/4 6.35 mm.",
   "Socket head: head dia ≈ 1.5 × major, head height = major. 1/4-20 SHCS: 0.375 in head, 0.25 in tall, 3/16 in hex key."
  ],
  "table": {
   "columns": [
    "size",
    "major_mm",
    "tpi",
    "clearance_mm",
    "tap_drill_mm"
   ],
   "rows": [
    [
     "#4-40",
     2.845,
     40,
     3.3,
     2.26
    ],
    [
     "#6-32",
     3.505,
     32,
     3.9,
     2.7
    ],
    [
     "#8-32",
     4.166,
     32,
     4.5,
     3.45
    ],
    [
     "1/4-20",
     6.35,
     20,
     6.8,
     5.11
    ]
   ]
  }
 },
 "sheet_text": "Imperial machine screws: #4-40, #6-32, #8-32, 1/4-20 — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/imperial-machine-screws/  (CC BY 4.0)\nBasis: ASME B18.6.3 / B18.3; Unified thread standard\nCatalog version: 2026-10-20\n\nSizes: see table below\n- Major diameters: #4 2.845 mm (0.112 in), #6 3.505 mm (0.138 in), #8 4.166 mm (0.164 in), 1/4 6.35 mm.\n- Socket head: head dia ≈ 1.5 × major, head height = major. 1/4-20 SHCS: 0.375 in head, 0.25 in tall, 3/16 in hex key.\n\nsize  major_mm  tpi  clearance_mm  tap_drill_mm\n#4-40  2.845  40  3.3  2.26\n#6-32  3.505  32  3.9  2.7\n#8-32  4.166  32  4.5  3.45\n1/4-20  6.35  20  6.8  5.11\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- McMaster-Carr: Machine screws (free STEP/IGES/STL per part, for your own design use; no redistribution) — STEP, IGES, STL, PDF — McMaster-Carr site terms: personal design use, no redistribution [verify license at link] — https://www.mcmaster.com/products/screws/machine-screws/\n- Wikipedia: Unified Thread Standard — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Unified_Thread_Standard\n\nFree files (CC BY 4.0, Xem Studio; STEP + STL, 18 parts): https://xemstudio.com/files/hardware/imperial-machine-screws/index.json\nAPI: https://xemstudio.com/api/geometry?object=imperial-machine-screws\n",
 "sources": [
  {
   "publisher": "McMaster-Carr",
   "title": "Machine screws (free STEP/IGES/STL per part, for your own design use; no redistribution)",
   "url": "https://www.mcmaster.com/products/screws/machine-screws/",
   "formats": [
    "STEP",
    "IGES",
    "STL",
    "PDF"
   ],
   "license": "McMaster-Carr site terms: personal design use, no redistribution",
   "license_verified": false,
   "hosted": false
  },
  {
   "publisher": "Wikipedia",
   "title": "Unified Thread Standard",
   "url": "https://en.wikipedia.org/wiki/Unified_Thread_Standard",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text)",
   "license_verified": true,
   "hosted": false
  }
 ],
 "xem": {
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  "sheet_free": true,
  "mesh_price_usd": null,
  "step_price_usd": null,
  "tolerance_mm": null
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 "related": [
  "socket-head-cap-screws-metric",
  "schedule-40-pipe"
 ],
 "faq": [
  {
   "q": "What is the diameter of a #4-40, #6-32 and #8-32 screw in mm?",
   "a": "#4-40: 2.845 mm (0.112 in). #6-32: 3.505 mm (0.138 in). #8-32: 4.166 mm (0.164 in). 1/4-20: 6.35 mm."
  },
  {
   "q": "What is the clearance hole for a #6-32 screw?",
   "a": "3.9 mm (0.1495 in, #25 drill); tap drill 2.7 mm (#36). #4-40: clearance 3.3 mm, tap 2.26 mm (#43). #8-32: clearance 4.5 mm, tap 3.45 mm (#29)."
  },
  {
   "q": "Is #6-32 the same as M3.5?",
   "a": "Close but not interchangeable: #6-32 is 3.505 mm with 32 TPI (0.794 mm pitch); M3.5 is 3.5 mm with a 0.6 mm pitch. Use metric nuts on metric screws."
  }
 ],
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