{
 "version": "2026-10-20",
 "license": "Dimension sheets: CC BY 4.0. Standard and published-size files: CC BY 4.0. Xem Studio's own designs (files_license = Xem Studio Design License): free to use and sell things from, not to redistribute as files — https://xemstudio.com/license/. Other publishers' files: their own license, linked beside them.",
 "slug": "lag-screws-hex-inch",
 "name": "Hex lag screws, 1/4 to 1/2 in (ASME B18.2.1): shank, head width and height, pilot holes + envelope models",
 "kind": "standard",
 "category": "Hardware",
 "group": "Fasteners",
 "year": null,
 "question": "What are the head size and pilot hole for a 3/8 lag screw?",
 "tags": [
  "lag screw",
  "lag bolt",
  "hex lag screw",
  "pilot hole",
  "asme b18.2.1",
  "fastener",
  "wood"
 ],
 "aliases": [
  "lag screw head size",
  "3/8 lag screw pilot hole",
  "1/4 lag screw wrench size",
  "lag bolt dimensions chart",
  "5/16 lag screw head width",
  "1/2 lag screw pilot hole hardwood",
  "lag screw head height",
  "lag screw threads per inch",
  "7/16 lag screw head size",
  "lag screw thread length",
  "b18.2.1 lag screw"
 ],
 "overall_mm": {
  "length": 22,
  "width": 19,
  "height": 84.9
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": false,
 "free_files": 5,
 "url": "https://xemstudio.com/objects/lag-screws-hex-inch/",
 "sheet_txt": "https://xemstudio.com/objects/lag-screws-hex-inch/sheet.txt",
 "sheet": {
  "basis": "AFT Fasteners' ASME B18.2.1 table with Engineers Edge, Fastenermart and McMaster-Carr as cross-checks; pilot holes from Fastenermart (by wood group) and from a Portland Bolt / Haydon table; five envelope models as files",
  "overall_mm": {
   "length": 22,
   "width": 19,
   "height": 84.9
  },
  "notes": [
   "Dimensions are inches, hex lag screws (the AFT table cites ASME B18.2.1-1996), 1/4 to 1/2: threads per inch; shank diameter E max / min; width across flats F (basic, then max / min); width across corners G max / min; head height H (basic, then max / min). AFT's flattened table was read by assigning columns from its layout, so check the standard if a figure matters. The same sizes agree with Fastenermart (F 7/16, 1/2, 9/16, 5/8, 3/4; H 11/64, 7/32, 1/4, 19/64, 11/32) and with McMaster-Carr's head heights (0.172, 0.219, 0.25, 0.344 for 1/4, 5/16, 3/8, 1/2).",
   "One disagreement: Engineers Edge prints a width across flats of 3/8 for the 1/4 lag screw, against 7/16 in AFT and Fastenermart (and 0.425–0.438 in AFT's max / min). Both are shown; the model uses 7/16. Thread length is a rule, not a column: AFT gives a minimum of half the screw length plus 0.50 in, capped at 5.00 in; Engineers Edge gives the same rule capped at 6.00 in. Both caps are as printed and they differ. Screws too short for the rule are threaded close to the head. AFT also prints length tolerance ±0.12 in to 6 in and ±0.25 in over 6 in, and a minimum shoulder length S (0.094, 0.125, 0.125, 0.156, 0.156 in).",
   "Pilot holes are not part of B18.2.1. Fastenermart: shank hole (equal to the nominal size), then threaded-portion pilot for softwood groups III and IV, medium wood group II and hardwood group I; the page calls them pilot, not lead holes, and does not explain a dagger on 7/16. Portland Bolt (credited to OBEC) and Haydon Bolts print one threaded-portion pilot per size, 15/64, 9/32, 5/16 for 3/8, 7/16, 1/2 (no 1/4 or 5/16 row); those equal Fastenermart's medium-wood column. Treat all as a guide, as Haydon does, and follow your project engineer or the screw maker.",
   "Files are Xem-drawn envelopes: a hexagon at the basic width across flats and the basic height (corners are F / cos 30°, which AFT's G max matches, e.g. 0.505 in for 1/4), on a plain cylinder at the nominal diameter; no thread, no chamfer, no washer face, no point. The 3 in length under the head is an example chosen by Xem for all five files, not a published length.",
   "McMaster-Carr sells lag screws with per-part STEP (it files them under hex head wood screws); the page is linked, not copied. Wood screws: wood-screws-flat-head-inch."
  ],
  "table": {
   "columns": [
    "size (in)",
    "TPI",
    "shank E max / min (in)",
    "across flats F, basic (AFT)",
    "F max / min (AFT, in)",
    "across flats F (Engineers Edge)",
    "across corners G max / min (in)",
    "head height H, basic (AFT)",
    "H max / min (AFT, in)",
    "shank hole (in)",
    "pilot, softwood III & IV (in)",
    "pilot, medium wood II (in)",
    "pilot, hardwood I (in)",
    "pilot (Portland Bolt / Haydon, in)"
   ],
   "rows": [
    [
     "1/4",
     "10",
     ".260 / .237",
     "7/16",
     ".438 / .425",
     "3/8",
     ".505 / .484",
     "11/64",
     ".188 / .150",
     "1/4",
     "3/32",
     "5/32",
     "3/16",
     "—"
    ],
    [
     "5/16",
     "9",
     ".324 / .298",
     "1/2",
     ".500 / .484",
     "1/2",
     ".577 / .552",
     "7/32",
     ".235 / .195",
     "5/16",
     "9/64",
     "3/16",
     "13/64",
     "—"
    ],
    [
     "3/8",
     "7",
     ".388 / .360",
     "9/16",
     ".562 / .544",
     "9/16",
     ".650 / .620",
     "1/4",
     ".268 / .226",
     "3/8",
     "11/64",
     "15/64",
     "1/4",
     "15/64"
    ],
    [
     "7/16",
     "7",
     ".452 / .421",
     "5/8",
     ".625 / .603",
     "5/8",
     ".722 / .687",
     "19/64",
     ".316 / .272",
     "7/16",
     "13/64",
     "9/32",
     "19/64",
     "9/32"
    ],
    [
     "1/2",
     "6",
     ".515 / .482",
     "3/4",
     ".750 / .725",
     "3/4",
     ".866 / .826",
     "11/32",
     ".364 / .302",
     "1/2",
     "15/64",
     "5/16",
     "11/32",
     "5/16"
    ]
   ]
  }
 },
 "sheet_text": "Hex lag screws, 1/4 to 1/2 in (ASME B18.2.1): shank, head width and height, pilot holes + envelope models — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/lag-screws-hex-inch/  (sheet CC BY 4.0)\nBasis: AFT Fasteners' ASME B18.2.1 table with Engineers Edge, Fastenermart and McMaster-Carr as cross-checks; pilot holes from Fastenermart (by wood group) and from a Portland Bolt / Haydon table; five envelope models as files\nCatalog version: 2026-10-20\n\nOverall (mm): length 22.0, width 19.0, height 84.9\n- Dimensions are inches, hex lag screws (the AFT table cites ASME B18.2.1-1996), 1/4 to 1/2: threads per inch; shank diameter E max / min; width across flats F (basic, then max / min); width across corners G max / min; head height H (basic, then max / min). AFT's flattened table was read by assigning columns from its layout, so check the standard if a figure matters. The same sizes agree with Fastenermart (F 7/16, 1/2, 9/16, 5/8, 3/4; H 11/64, 7/32, 1/4, 19/64, 11/32) and with McMaster-Carr's head heights (0.172, 0.219, 0.25, 0.344 for 1/4, 5/16, 3/8, 1/2).\n- One disagreement: Engineers Edge prints a width across flats of 3/8 for the 1/4 lag screw, against 7/16 in AFT and Fastenermart (and 0.425–0.438 in AFT's max / min). Both are shown; the model uses 7/16. Thread length is a rule, not a column: AFT gives a minimum of half the screw length plus 0.50 in, capped at 5.00 in; Engineers Edge gives the same rule capped at 6.00 in. Both caps are as printed and they differ. Screws too short for the rule are threaded close to the head. AFT also prints length tolerance ±0.12 in to 6 in and ±0.25 in over 6 in, and a minimum shoulder length S (0.094, 0.125, 0.125, 0.156, 0.156 in).\n- Pilot holes are not part of B18.2.1. Fastenermart: shank hole (equal to the nominal size), then threaded-portion pilot for softwood groups III and IV, medium wood group II and hardwood group I; the page calls them pilot, not lead holes, and does not explain a dagger on 7/16. Portland Bolt (credited to OBEC) and Haydon Bolts print one threaded-portion pilot per size, 15/64, 9/32, 5/16 for 3/8, 7/16, 1/2 (no 1/4 or 5/16 row); those equal Fastenermart's medium-wood column. Treat all as a guide, as Haydon does, and follow your project engineer or the screw maker.\n- Files are Xem-drawn envelopes: a hexagon at the basic width across flats and the basic height (corners are F / cos 30°, which AFT's G max matches, e.g. 0.505 in for 1/4), on a plain cylinder at the nominal diameter; no thread, no chamfer, no washer face, no point. The 3 in length under the head is an example chosen by Xem for all five files, not a published length.\n- McMaster-Carr sells lag screws with per-part STEP (it files them under hex head wood screws); the page is linked, not copied. Wood screws: wood-screws-flat-head-inch.\n\nsize (in)  TPI  shank E max / min (in)  across flats F, basic (AFT)  F max / min (AFT, in)  across flats F (Engineers Edge)  across corners G max / min (in)  head height H, basic (AFT)  H max / min (AFT, in)  shank hole (in)  pilot, softwood III & IV (in)  pilot, medium wood II (in)  pilot, hardwood I (in)  pilot (Portland Bolt / Haydon, in)\n1/4  10  .260 / .237  7/16  .438 / .425  3/8  .505 / .484  11/64  .188 / .150  1/4  3/32  5/32  3/16  —\n5/16  9  .324 / .298  1/2  .500 / .484  1/2  .577 / .552  7/32  .235 / .195  5/16  9/64  3/16  13/64  —\n3/8  7  .388 / .360  9/16  .562 / .544  9/16  .650 / .620  1/4  .268 / .226  3/8  11/64  15/64  1/4  15/64\n7/16  7  .452 / .421  5/8  .625 / .603  5/8  .722 / .687  19/64  .316 / .272  7/16  13/64  9/32  19/64  9/32\n1/2  6  .515 / .482  3/4  .750 / .725  3/4  .866 / .826  11/32  .364 / .302  1/2  15/64  5/16  11/32  5/16\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- AFT Fasteners: Lag screws dimensions and mechanical properties (ASME B18.2.1-1996): E shank, F width across flats, G across corners, H head height, S shoulder length, thread-length rule — web — Publisher's page; dimensions are facts — https://www.aftfasteners.com/lag-screws-dimensions-and-mechanical-properties/\n- Engineers Edge: Standard hex lag screws: shank diameter E, head width across flats F, head height H, threads per inch, thread-length rule — web — Publisher's page; dimensions are facts — https://ns1.engineersedge.com/hardware/standard_hex_lag_screws_16077.htm\n- Fastenermart: Lag screws: pilot hole sizes by wood group (shank hole, softwood groups III & IV, medium group II, hardwood group I) and head dimensions — web — Publisher's page; dimensions are facts — https://fastenermart.com/lag-screws.html\n- Portland Bolt (table credited to OBEC Consulting Engineers): Pilot hole sizes for lag screws: unthreaded shank portion and threaded-portion pilot, 3/8 to 1/2 in — web — Distributor table; numbers only — https://portlandbolt.com/print/?table=1176\n- Haydon Bolts: Lag bolt pilot hole diameter: shank (unthreaded) and pilot hole, 3/8 to 1/2 in (same values as Portland Bolt's table) — web — Maker page; numbers only — https://haydonbolts.com/?p=255\n- McMaster-Carr: Stainless steel hex head lag screws (McMaster files these as hex head wood screws) (free STEP/IGES per part, for your own design use; no redistribution) — STEP, IGES, PDF — McMaster-Carr site terms: personal design use, no redistribution [verify license at link] — https://www.mcmaster.com/stainless-steel-hex-head-lag-screws\n\nFree files (CC BY 4.0, Xem Studio; STEP + STL, 5 parts): https://xemstudio.com/files/hardware/lag-screws-hex-inch/index.json\nAPI: https://xemstudio.com/api/geometry?object=lag-screws-hex-inch\n",
 "sources": [
  {
   "publisher": "AFT Fasteners",
   "title": "Lag screws dimensions and mechanical properties (ASME B18.2.1-1996): E shank, F width across flats, G across corners, H head height, S shoulder length, thread-length rule",
   "url": "https://www.aftfasteners.com/lag-screws-dimensions-and-mechanical-properties/",
   "formats": [
    "web"
   ],
   "license": "Publisher's page; dimensions are facts",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Engineers Edge",
   "title": "Standard hex lag screws: shank diameter E, head width across flats F, head height H, threads per inch, thread-length rule",
   "url": "https://ns1.engineersedge.com/hardware/standard_hex_lag_screws_16077.htm",
   "formats": [
    "web"
   ],
   "license": "Publisher's page; dimensions are facts",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Fastenermart",
   "title": "Lag screws: pilot hole sizes by wood group (shank hole, softwood groups III & IV, medium group II, hardwood group I) and head dimensions",
   "url": "https://fastenermart.com/lag-screws.html",
   "formats": [
    "web"
   ],
   "license": "Publisher's page; dimensions are facts",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Portland Bolt (table credited to OBEC Consulting Engineers)",
   "title": "Pilot hole sizes for lag screws: unthreaded shank portion and threaded-portion pilot, 3/8 to 1/2 in",
   "url": "https://portlandbolt.com/print/?table=1176",
   "formats": [
    "web"
   ],
   "license": "Distributor table; numbers only",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Haydon Bolts",
   "title": "Lag bolt pilot hole diameter: shank (unthreaded) and pilot hole, 3/8 to 1/2 in (same values as Portland Bolt's table)",
   "url": "https://haydonbolts.com/?p=255",
   "formats": [
    "web"
   ],
   "license": "Maker page; numbers only",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "McMaster-Carr",
   "title": "Stainless steel hex head lag screws (McMaster files these as hex head wood screws) (free STEP/IGES per part, for your own design use; no redistribution)",
   "url": "https://www.mcmaster.com/stainless-steel-hex-head-lag-screws",
   "formats": [
    "STEP",
    "IGES",
    "PDF"
   ],
   "license": "McMaster-Carr site terms: personal design use, no redistribution",
   "license_verified": false,
   "hosted": false
  }
 ],
 "xem": {
  "status": "free-files",
  "sheet_free": true,
  "mesh_price_usd": null,
  "step_price_usd": null,
  "tolerance_mm": null
 },
 "related": [
  "wood-screws-flat-head-inch",
  "hex-bolts-inch",
  "hex-nuts-inch",
  "shoulder-eye-bolts-inch",
  "socket-head-cap-screws-inch"
 ],
 "fits": [],
 "dimensions": "exact (nominal, no tolerance added)",
 "dimension_rule": "All geometry on Xem Studio is exact (nominal, true size) with no tolerance added. Where a part meets another part, the object lists its mating features (feature, exact size, what it mates with, fit class: press, slide, run, socket, clamp or designed). Apply your process's allowance to those features only; 'designed' gaps are part of the design and stay as drawn. Typical accuracy by process and ISO 286 fits: https://xemstudio.com/tolerances/",
 "mating": [
  {
   "feature": "shank",
   "exact": "1/4, 5/16, 3/8, 7/16, 1/2 in",
   "mates": "shank hole = nominal size; pilot softwood III & IV 3/32, 9/64, 11/64, 13/64, 15/64; medium wood II 5/32, 3/16, 15/64, 9/32, 5/16; hardwood I 3/16, 13/64, 1/4, 19/64, 11/32 in (Fastenermart)",
   "fit": "designed",
   "files": "lag-screw-"
  },
  {
   "feature": "head",
   "exact": "hex across flats × height: 7/16 × 11/64 (1/4), 1/2 × 7/32, 9/16 × 1/4, 5/8 × 19/64, 3/4 × 11/32 in",
   "mates": "hex pocket or socket space",
   "fit": "slide",
   "files": "lag-screw-"
  }
 ],
 "fit_classes": {
  "press": "stays put: pin, tube, bearing or magnet held by interference. ISO 286 equivalent: H7/p6 (locational interference) or tighter.",
  "slide": "assembles by hand and is held by a grub, pinch or clamp: shaft in a hub, rod in a socket, spigot in a bore. ISO 286 equivalent: H7/g6 or H7/h6.",
  "run": "turns or slides in use: pin in a link, rod through a guide. ISO 286 equivalent: H8/f7 (close running).",
  "socket": "large sliding fit: syringe barrel, sleeve, bobbin in a bore. ISO 286 equivalent: H9/d9 (free running) or looser.",
  "clamp": "split part that closes on the mating part with screws: make it at size.",
  "designed": "a gap that is part of the design (piston fit option, displacer gap, air gap): do not change."
 },
 "faq": [
  {
   "q": "What size wrench for a 3/8 lag screw?",
   "a": "9/16 in across flats (basic) in AFT's B18.2.1 table, Engineers Edge and Fastenermart; head height 1/4 in."
  },
  {
   "q": "What pilot hole for a 1/2 lag screw?",
   "a": "Fastenermart: 15/64 softwood (groups III & IV), 5/16 medium wood, 11/32 hardwood; Portland Bolt and Haydon print 5/16 for the threaded portion. The shank hole is 1/2 in."
  },
  {
   "q": "How much of a lag screw is threaded?",
   "a": "At least half the length plus 0.50 in, capped at 5.00 in (AFT) or 6.00 in (Engineers Edge); short screws are threaded close to the head."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "lag-screw-1-4-hex-3in-envelope",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/lag-screws-hex-inch/lag-screw-1-4-hex-3in-envelope.step",
   "stl": "https://xemstudio.com/files/hardware/lag-screws-hex-inch/lag-screw-1-4-hex-3in-envelope.stl",
   "note": "1/4 hex lag screw envelope: hex head 7/16 in across flats (basic) × 11/64 in high (basic) on a plain Ø6.35 mm (1/4 in nominal) shank, example length 3 in (76.2 mm) under the head (Xem's choice); no thread, chamfer, washer face or point"
  },
  {
   "file": "lag-screw-5-16-hex-3in-envelope",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/lag-screws-hex-inch/lag-screw-5-16-hex-3in-envelope.step",
   "stl": "https://xemstudio.com/files/hardware/lag-screws-hex-inch/lag-screw-5-16-hex-3in-envelope.stl",
   "note": "5/16 hex lag screw envelope: hex head 1/2 in across flats (basic) × 7/32 in high (basic) on a plain Ø7.94 mm (5/16 in nominal) shank, example length 3 in (76.2 mm) under the head (Xem's choice); no thread, chamfer, washer face or point"
  },
  {
   "file": "lag-screw-3-8-hex-3in-envelope",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/lag-screws-hex-inch/lag-screw-3-8-hex-3in-envelope.step",
   "stl": "https://xemstudio.com/files/hardware/lag-screws-hex-inch/lag-screw-3-8-hex-3in-envelope.stl",
   "note": "3/8 hex lag screw envelope: hex head 9/16 in across flats (basic) × 1/4 in high (basic) on a plain Ø9.52 mm (3/8 in nominal) shank, example length 3 in (76.2 mm) under the head (Xem's choice); no thread, chamfer, washer face or point"
  },
  {
   "file": "lag-screw-7-16-hex-3in-envelope",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/lag-screws-hex-inch/lag-screw-7-16-hex-3in-envelope.step",
   "stl": "https://xemstudio.com/files/hardware/lag-screws-hex-inch/lag-screw-7-16-hex-3in-envelope.stl",
   "note": "7/16 hex lag screw envelope: hex head 5/8 in across flats (basic) × 19/64 in high (basic) on a plain Ø11.11 mm (7/16 in nominal) shank, example length 3 in (76.2 mm) under the head (Xem's choice); no thread, chamfer, washer face or point"
  },
  {
   "file": "lag-screw-1-2-hex-3in-envelope",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/lag-screws-hex-inch/lag-screw-1-2-hex-3in-envelope.step",
   "stl": "https://xemstudio.com/files/hardware/lag-screws-hex-inch/lag-screw-1-2-hex-3in-envelope.stl",
   "note": "1/2 hex lag screw envelope: hex head 3/4 in across flats (basic) × 11/32 in high (basic) on a plain Ø12.70 mm (1/2 in nominal) shank, example length 3 in (76.2 mm) under the head (Xem's choice); no thread, chamfer, washer face or point"
  }
 ],
 "markdown": "https://xemstudio.com/objects/lag-screws-hex-inch/index.md"
}