{
 "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": "nut-pocket-flywheels",
 "name": "Flywheels Ø100–Ø200 with hex-nut rim pockets",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Drives & mechanisms",
 "year": null,
 "question": "How is a flywheel with hex nut pockets in the rim laid out?",
 "tags": [
  "flywheel",
  "nut",
  "inertia",
  "counterweight",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "flywheel with nut pockets",
  "weighted flywheel",
  "flywheel hex nut weights",
  "stirling engine flywheel 150mm",
  "heavy flywheel model engine"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": true,
 "free_files": 19,
 "url": "https://xemstudio.com/objects/nut-pocket-flywheels/",
 "sheet_txt": "https://xemstudio.com/objects/nut-pocket-flywheels/sheet.txt",
 "sheet": {
  "basis": "Rim of hex pockets at the nut's across-flats, one flat facing out, depth = nut thickness; pocket count a multiple of 6",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "A rim of hex pockets, each at the nut's exact across-flats with one flat facing outward and as deep as the nut is thick, on a 1.5 mm floor; a nut sits flush with the face.",
   "Pocket counts are multiples of six: all, every other one, every third or one half can be filled and the wheel stays balanced, or one half only makes a counterweight opposite the crank pin.",
   "Rim thickness = nut thickness + 1.5; rim radial width = across-flats + 6. A 4 mm web with six round windows joins the rim to a hub Ø20 (Ø3 and Ø5 bore) or Ø22 (Ø8 bore), 4 mm taller than the rim.",
   "Each hub has a radial Ø2.5 hole (M3 tap drill) for a grub on the shaft's D-flat. Ø3 hubs exist on the Ø100 and Ø120 wheels only."
  ],
  "table": {
   "columns": [
    "OD",
    "nut",
    "pockets",
    "pocket circle R",
    "rim thickness",
    "rim width",
    "hub",
    "bores"
   ],
   "rows": [
    [
     100,
     "M8",
     12,
     40.5,
     8.3,
     19,
     "Ø20 / Ø22 × 12.3",
     "3 / 5 / 8"
    ],
    [
     120,
     "M10",
     12,
     49,
     9.9,
     22,
     "Ø20 / Ø22 × 13.9",
     "3 / 5 / 8"
    ],
    [
     120,
     "3/8 in",
     12,
     49.9,
     9.8,
     20.3,
     "Ø20 / Ø22 × 13.8",
     "3 / 5 / 8"
    ],
    [
     150,
     "M10",
     18,
     64,
     9.9,
     22,
     "Ø20 / Ø22 × 13.9",
     "5 / 8"
    ],
    [
     150,
     "M12",
     12,
     63,
     12.3,
     24,
     "Ø20 / Ø22 × 16.3",
     "5 / 8"
    ],
    [
     150,
     "1/2 in",
     12,
     62.5,
     12.6,
     25.1,
     "Ø20 / Ø22 × 16.6",
     "5 / 8"
    ],
    [
     200,
     "M12",
     18,
     88,
     12.3,
     24,
     "Ø20 / Ø22 × 16.3",
     "5 / 8"
    ],
    [
     200,
     "1/2 in",
     18,
     87.5,
     12.6,
     25.1,
     "Ø20 / Ø22 × 16.6",
     "5 / 8"
    ]
   ]
  }
 },
 "sheet_text": "Flywheels Ø100–Ø200 with hex-nut rim pockets — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/nut-pocket-flywheels/  (CC BY 4.0)\nBasis: Rim of hex pockets at the nut's across-flats, one flat facing out, depth = nut thickness; pocket count a multiple of 6\nCatalog version: 2026-10-20\n\nSizes: see table below\n- A rim of hex pockets, each at the nut's exact across-flats with one flat facing outward and as deep as the nut is thick, on a 1.5 mm floor; a nut sits flush with the face.\n- Pocket counts are multiples of six: all, every other one, every third or one half can be filled and the wheel stays balanced, or one half only makes a counterweight opposite the crank pin.\n- Rim thickness = nut thickness + 1.5; rim radial width = across-flats + 6. A 4 mm web with six round windows joins the rim to a hub Ø20 (Ø3 and Ø5 bore) or Ø22 (Ø8 bore), 4 mm taller than the rim.\n- Each hub has a radial Ø2.5 hole (M3 tap drill) for a grub on the shaft's D-flat. Ø3 hubs exist on the Ø100 and Ø120 wheels only.\n\nOD  nut  pockets  pocket circle R  rim thickness  rim width  hub  bores\n100  M8  12  40.5  8.3  19.0  Ø20 / Ø22 × 12.3  3 / 5 / 8\n120  M10  12  49.0  9.9  22.0  Ø20 / Ø22 × 13.9  3 / 5 / 8\n120  3/8 in  12  49.9  9.8  20.3  Ø20 / Ø22 × 13.8  3 / 5 / 8\n150  M10  18  64.0  9.9  22.0  Ø20 / Ø22 × 13.9  5 / 8\n150  M12  12  63.0  12.3  24.0  Ø20 / Ø22 × 16.3  5 / 8\n150  1/2 in  12  62.5  12.6  25.1  Ø20 / Ø22 × 16.6  5 / 8\n200  M12  18  88.0  12.3  24.0  Ø20 / Ø22 × 16.3  5 / 8\n200  1/2 in  18  87.5  12.6  25.1  Ø20 / Ø22 × 16.6  5 / 8\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- ISO: ISO 4032 Hexagon regular nuts (style 1) — standard — ISO [verify license at link] — https://www.iso.org/standard/72624.html\n- ASME: ASME B18.2.2 Nuts for general applications — standard — ASME [verify license at link] — https://www.asme.org/codes-standards/find-codes-standards/b18-2-2-nuts-for-general-applications-machine-screw-nuts-hex-square-hex-flange-coupling-nuts-(inch-series)\n- Long Earth Society: Engine builds — web, video — LES site — https://longearthsociety.com/engineering/\n\nFree files (CC BY 4.0, Xem Studio; STEP + STL, 19 parts): https://xemstudio.com/files/hardware/nut-pocket-flywheels/index.json\nAPI: https://xemstudio.com/api/geometry?object=nut-pocket-flywheels\n",
 "sources": [
  {
   "publisher": "ISO",
   "title": "ISO 4032 Hexagon regular nuts (style 1)",
   "url": "https://www.iso.org/standard/72624.html",
   "formats": [
    "standard"
   ],
   "license": "ISO",
   "license_verified": false,
   "hosted": false
  },
  {
   "publisher": "ASME",
   "title": "ASME B18.2.2 Nuts for general applications",
   "url": "https://www.asme.org/codes-standards/find-codes-standards/b18-2-2-nuts-for-general-applications-machine-screw-nuts-hex-square-hex-flange-coupling-nuts-(inch-series)",
   "formats": [
    "standard"
   ],
   "license": "ASME",
   "license_verified": false,
   "hosted": false
  },
  {
   "publisher": "Long Earth Society",
   "title": "Engine builds",
   "url": "https://longearthsociety.com/engineering/",
   "formats": [
    "web",
    "video"
   ],
   "license": "LES site",
   "license_verified": true,
   "hosted": false
  }
 ],
 "xem": {
  "status": "free-files",
  "sheet_free": true,
  "mesh_price_usd": null,
  "step_price_usd": null,
  "tolerance_mm": null
 },
 "related": [
  "hex-nut-weights",
  "spoked-flywheels",
  "stirling-crankshafts",
  "hex-nuts-metric",
  "counterweighted-crank-discs"
 ],
 "fits": [
  {
   "role": "Goes in or on",
   "items": [
    {
     "slug": "stirling-crankshafts",
     "why": "Ø3 / Ø5 / Ø8 hub, M3 grub on the flat"
    },
    {
     "slug": "crank-stands-625",
     "why": "on the Ø5 shaft outside the stand"
    }
   ]
  },
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "hex-nut-weights",
     "why": "nut in each hex pocket, one flat outward"
    }
   ]
  },
  {
   "role": "Alternatives",
   "items": [
    {
     "slug": "spoked-flywheels",
     "why": "plain spoked wheel"
    }
   ]
  },
  {
   "role": "Also needed",
   "items": [
    {
     "slug": "set-screws-metric",
     "why": "M3 grub"
    }
   ]
  }
 ],
 "dimensions": "exact (nominal, no printing tolerance)",
 "dimension_rule": "All geometry on Xem Studio is exact (nominal, true size) with no printing tolerance. 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.",
 "mating": [
  {
   "feature": "hub bore",
   "exact": "Ø3 / Ø5 / Ø8",
   "mates": "D-flat crankshaft (M3 grub)",
   "fit": "slide",
   "files": "flywheel-"
  },
  {
   "feature": "rim pockets",
   "exact": "nut across-corners",
   "mates": "hex nut, one flat outward",
   "fit": "press",
   "files": "flywheel-"
  },
  {
   "feature": "grub hole",
   "exact": "Ø2.5",
   "mates": "M3 tap drill",
   "fit": "designed",
   "files": "flywheel-"
  }
 ],
 "fit_classes": {
  "press": "stays put: pin, tube, bearing or magnet held by interference. Typical FDM: hole +0.0 to +0.1 mm on diameter.",
  "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. Typical FDM: +0.2 mm.",
  "run": "turns or slides in use: pin in a link, rod through a guide. Typical FDM: +0.3 mm.",
  "socket": "large sliding fit: syringe barrel, sleeve, bobbin in a bore. Typical FDM: +0.3 mm.",
  "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": "How many nuts does the Ø150 flywheel hold?",
   "a": "18 M10 nuts on the M10 wheel (R64), or 12 on the M12 and 1/2 in wheels."
  },
  {
   "q": "Can I fill only some pockets?",
   "a": "Yes: pocket counts are multiples of six, so all, alternate, every third or one half all leave the wheel balanced, and one half only is a counterweight."
  },
  {
   "q": "Metric or inch nuts?",
   "a": "The Ø120, Ø150 and Ø200 wheels come in 3/8 in and 1/2 in versions as well as M10 and M12."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "flywheel-100-m8-b3",
   "formats": [
    "step",
    "stl"
   ],
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   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-100-m8-b3.step",
   "stl": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-100-m8-b3.stl",
   "note": "Ø100 flywheel, 12 pockets for M8 hex nuts at R40.5 (one flat facing out), Ø3 hub with M3 grub, 8.3 thick rim; full set ≈ 67 g of nuts, +1.1 kg·cm²"
  },
  {
   "file": "flywheel-100-m8-b5",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-100-m8-b5.step",
   "stl": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-100-m8-b5.stl",
   "note": "Ø100 flywheel, 12 pockets for M8 hex nuts at R40.5 (one flat facing out), Ø5 hub with M3 grub, 8.3 thick rim; full set ≈ 67 g of nuts, +1.1 kg·cm²"
  },
  {
   "file": "flywheel-100-m8-b8",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-100-m8-b8.step",
   "stl": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-100-m8-b8.stl",
   "note": "Ø100 flywheel, 12 pockets for M8 hex nuts at R40.5 (one flat facing out), Ø8 hub with M3 grub, 8.3 thick rim; full set ≈ 67 g of nuts, +1.1 kg·cm²"
  },
  {
   "file": "flywheel-120-m10-b3",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-120-m10-b3.step",
   "stl": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-120-m10-b3.stl",
   "note": "Ø120 flywheel, 12 pockets for M10 hex nuts at R49.0 (one flat facing out), Ø3 hub with M3 grub, 9.9 thick rim; full set ≈ 124 g of nuts, +3.0 kg·cm²"
  },
  {
   "file": "flywheel-120-m10-b5",
   "formats": [
    "step",
    "stl"
   ],
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   "license": "CC BY 4.0 (Xem Studio)",
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   "stl": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-120-m10-b5.stl",
   "note": "Ø120 flywheel, 12 pockets for M10 hex nuts at R49.0 (one flat facing out), Ø5 hub with M3 grub, 9.9 thick rim; full set ≈ 124 g of nuts, +3.0 kg·cm²"
  },
  {
   "file": "flywheel-120-m10-b8",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
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   "stl": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-120-m10-b8.stl",
   "note": "Ø120 flywheel, 12 pockets for M10 hex nuts at R49.0 (one flat facing out), Ø8 hub with M3 grub, 9.9 thick rim; full set ≈ 124 g of nuts, +3.0 kg·cm²"
  },
  {
   "file": "flywheel-120-3-8in-b3",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
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   "stl": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-120-3-8in-b3.stl",
   "note": "Ø120 flywheel, 12 pockets for 3/8 in hex nuts at R49.9 (one flat facing out), Ø3 hub with M3 grub, 9.8 thick rim; full set ≈ 93 g of nuts, +2.3 kg·cm²"
  },
  {
   "file": "flywheel-120-3-8in-b5",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
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   "stl": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-120-3-8in-b5.stl",
   "note": "Ø120 flywheel, 12 pockets for 3/8 in hex nuts at R49.9 (one flat facing out), Ø5 hub with M3 grub, 9.8 thick rim; full set ≈ 93 g of nuts, +2.3 kg·cm²"
  },
  {
   "file": "flywheel-120-3-8in-b8",
   "formats": [
    "step",
    "stl"
   ],
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   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-120-3-8in-b8.step",
   "stl": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-120-3-8in-b8.stl",
   "note": "Ø120 flywheel, 12 pockets for 3/8 in hex nuts at R49.9 (one flat facing out), Ø8 hub with M3 grub, 9.8 thick rim; full set ≈ 93 g of nuts, +2.3 kg·cm²"
  },
  {
   "file": "flywheel-150-m10-b5",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-150-m10-b5.step",
   "stl": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-150-m10-b5.stl",
   "note": "Ø150 flywheel, 18 pockets for M10 hex nuts at R64.0 (one flat facing out), Ø5 hub with M3 grub, 9.9 thick rim; full set ≈ 186 g of nuts, +7.6 kg·cm²"
  },
  {
   "file": "flywheel-150-m10-b8",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-150-m10-b8.step",
   "stl": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-150-m10-b8.stl",
   "note": "Ø150 flywheel, 18 pockets for M10 hex nuts at R64.0 (one flat facing out), Ø8 hub with M3 grub, 9.9 thick rim; full set ≈ 186 g of nuts, +7.6 kg·cm²"
  },
  {
   "file": "flywheel-150-m12-b5",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-150-m12-b5.step",
   "stl": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-150-m12-b5.stl",
   "note": "Ø150 flywheel, 12 pockets for M12 hex nuts at R63.0 (one flat facing out), Ø5 hub with M3 grub, 12.3 thick rim; full set ≈ 192 g of nuts, +7.6 kg·cm²"
  },
  {
   "file": "flywheel-150-m12-b8",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-150-m12-b8.step",
   "stl": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-150-m12-b8.stl",
   "note": "Ø150 flywheel, 12 pockets for M12 hex nuts at R63.0 (one flat facing out), Ø8 hub with M3 grub, 12.3 thick rim; full set ≈ 192 g of nuts, +7.6 kg·cm²"
  },
  {
   "file": "flywheel-150-1-2in-b5",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-150-1-2in-b5.step",
   "stl": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-150-1-2in-b5.stl",
   "note": "Ø150 flywheel, 12 pockets for 1/2 in hex nuts at R62.5 (one flat facing out), Ø5 hub with M3 grub, 12.6 thick rim; full set ≈ 221 g of nuts, +8.6 kg·cm²"
  },
  {
   "file": "flywheel-150-1-2in-b8",
   "formats": [
    "step",
    "stl"
   ],
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   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-150-1-2in-b8.step",
   "stl": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-150-1-2in-b8.stl",
   "note": "Ø150 flywheel, 12 pockets for 1/2 in hex nuts at R62.5 (one flat facing out), Ø8 hub with M3 grub, 12.6 thick rim; full set ≈ 221 g of nuts, +8.6 kg·cm²"
  },
  {
   "file": "flywheel-200-m12-b5",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-200-m12-b5.step",
   "stl": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-200-m12-b5.stl",
   "note": "Ø200 flywheel, 18 pockets for M12 hex nuts at R88.0 (one flat facing out), Ø5 hub with M3 grub, 12.3 thick rim; full set ≈ 288 g of nuts, +22.3 kg·cm²"
  },
  {
   "file": "flywheel-200-m12-b8",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-200-m12-b8.step",
   "stl": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-200-m12-b8.stl",
   "note": "Ø200 flywheel, 18 pockets for M12 hex nuts at R88.0 (one flat facing out), Ø8 hub with M3 grub, 12.3 thick rim; full set ≈ 288 g of nuts, +22.3 kg·cm²"
  },
  {
   "file": "flywheel-200-1-2in-b5",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-200-1-2in-b5.step",
   "stl": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-200-1-2in-b5.stl",
   "note": "Ø200 flywheel, 18 pockets for 1/2 in hex nuts at R87.5 (one flat facing out), Ø5 hub with M3 grub, 12.6 thick rim; full set ≈ 332 g of nuts, +25.4 kg·cm²"
  },
  {
   "file": "flywheel-200-1-2in-b8",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-200-1-2in-b8.step",
   "stl": "https://xemstudio.com/files/hardware/nut-weighted-flywheels/flywheel-200-1-2in-b8.stl",
   "note": "Ø200 flywheel, 18 pockets for 1/2 in hex nuts at R87.5 (one flat facing out), Ø8 hub with M3 grub, 12.6 thick rim; full set ≈ 332 g of nuts, +25.4 kg·cm²"
  }
 ],
 "markdown": "https://xemstudio.com/objects/nut-pocket-flywheels/index.md"
}