{
 "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": "flywheel-disc-hub",
 "name": "CD and HDD-platter flywheel hubs: Ø15 and Ø25 spigots for Ø3 / 5 / 8 shafts",
 "kind": "standard",
 "category": "Stirling engines",
 "group": "Can & LTD engines",
 "year": null,
 "question": "What are the dimensions of a hub that mounts a CD or hard-drive platter on a shaft?",
 "tags": [
  "flywheel",
  "hub",
  "cd",
  "hdd platter",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "cd flywheel hub",
  "cd hub 3mm shaft",
  "hard drive platter hub",
  "cd to shaft adapter stl"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": true,
 "free_files": 5,
 "url": "https://xemstudio.com/objects/flywheel-disc-hub/",
 "sheet_txt": "https://xemstudio.com/objects/flywheel-disc-hub/sheet.txt",
 "sheet": {
  "basis": "Spigot at the disc's centre hole (CD Ø15, 3.5 in HDD platter Ø25); bore at the shaft; M3 tap drill Ø2.5 for the set screw",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "A hub that carries a CD/DVD or a 3.5 in hard-drive platter as a flywheel. The spigot is the disc's centre hole exactly: Ø15 for a CD, Ø25 for a platter, 1.3 tall.",
   "As drawn, the spigot sits between a Ø(spigot + 8) × 2 collar below and the Ø(spigot + 8) hub body above (Ø23 for CD hubs, Ø33 for platter hubs), 12 mm overall.",
   "Bores: Ø3, Ø5 or Ø8 (fit: slide) for the shaft, with a Ø2.5 radial hole (M3 tap size) 6 mm above the lower collar for an M3 set screw."
  ],
  "table": {
   "columns": [
    "file",
    "disc",
    "spigot",
    "bore",
    "outside",
    "height"
   ],
   "rows": [
    [
     "hub-cd-15-to-3",
     "CD / DVD",
     15,
     3,
     23,
     12
    ],
    [
     "hub-cd-15-to-5",
     "CD / DVD",
     15,
     5,
     23,
     12
    ],
    [
     "hub-cd-15-to-8",
     "CD / DVD",
     15,
     8,
     23,
     12
    ],
    [
     "hub-platter-25-to-5",
     "3.5 in HDD platter",
     25,
     5,
     33,
     12
    ],
    [
     "hub-platter-25-to-8",
     "3.5 in HDD platter",
     25,
     8,
     33,
     12
    ]
   ]
  }
 },
 "sheet_text": "CD and HDD-platter flywheel hubs: Ø15 and Ø25 spigots for Ø3 / 5 / 8 shafts — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/flywheel-disc-hub/  (CC BY 4.0)\nBasis: Spigot at the disc's centre hole (CD Ø15, 3.5 in HDD platter Ø25); bore at the shaft; M3 tap drill Ø2.5 for the set screw\nCatalog version: 2026-10-20\n\nSizes: see table below\n- A hub that carries a CD/DVD or a 3.5 in hard-drive platter as a flywheel. The spigot is the disc's centre hole exactly: Ø15 for a CD, Ø25 for a platter, 1.3 tall.\n- As drawn, the spigot sits between a Ø(spigot + 8) × 2 collar below and the Ø(spigot + 8) hub body above (Ø23 for CD hubs, Ø33 for platter hubs), 12 mm overall.\n- Bores: Ø3, Ø5 or Ø8 (fit: slide) for the shaft, with a Ø2.5 radial hole (M3 tap size) 6 mm above the lower collar for an M3 set screw.\n\nfile  disc  spigot  bore  outside  height\nhub-cd-15-to-3  CD / DVD  15  3  23  12\nhub-cd-15-to-5  CD / DVD  15  5  23  12\nhub-cd-15-to-8  CD / DVD  15  8  23  12\nhub-platter-25-to-5  3.5 in HDD platter  25  5  33  12\nhub-platter-25-to-8  3.5 in HDD platter  25  8  33  12\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Wikipedia: Stirling engine — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Stirling_engine\n- Long Earth Society: Can engine build — video, web — LES site — https://longearthsociety.com/engineering/\n- Long Earth Society: Engine builds (videos and write-ups) — web, video — LES site — https://longearthsociety.com/engineering/\n\nFree files (CC BY 4.0, Xem Studio; STEP + STL, 5 parts): https://xemstudio.com/files/hardware/flywheel-disc-hub/index.json\nAPI: https://xemstudio.com/api/geometry?object=flywheel-disc-hub\n",
 "sources": [
  {
   "publisher": "Wikipedia",
   "title": "Stirling engine",
   "url": "https://en.wikipedia.org/wiki/Stirling_engine",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text)",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Long Earth Society",
   "title": "Can engine build",
   "url": "https://longearthsociety.com/engineering/",
   "formats": [
    "video",
    "web"
   ],
   "license": "LES site",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Long Earth Society",
   "title": "Engine builds (videos and write-ups)",
   "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": [
  "cd-dvd-discs",
  "can-engine-crank-stand",
  "nut-pocket-flywheels",
  "stirling-crankshafts",
  "list-can-engine"
 ],
 "fits": [
  {
   "role": "Goes in or on",
   "items": [
    {
     "slug": "cd-dvd-discs",
     "why": "Ø15 / Ø25 spigot in the disc's centre hole"
    }
   ]
  },
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "stirling-crankshafts",
     "why": "Ø3 / Ø5 / Ø8 shaft in the bore"
    },
    {
     "slug": "craft-sticks",
     "why": "Ø3 skewer in the Ø3 bore"
    }
   ]
  },
  {
   "role": "Alternatives",
   "items": [
    {
     "slug": "nut-pocket-flywheels",
     "why": "a nut-weighted flywheel instead of a disc"
    }
   ]
  },
  {
   "role": "Also needed",
   "items": [
    {
     "slug": "set-screws-metric",
     "why": "M3 set screw in the Ø2.5 hole"
    }
   ]
  }
 ],
 "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": "CD hub spigot",
   "exact": "Ø15",
   "mates": "CD / DVD centre hole",
   "fit": "press",
   "files": "hub-cd-"
  },
  {
   "feature": "platter hub spigot",
   "exact": "Ø25",
   "mates": "3.5 in HDD platter hole",
   "fit": "press",
   "files": "hub-platter-"
  },
  {
   "feature": "hub bore",
   "exact": "Ø3 / Ø5 / Ø8",
   "mates": "shaft (M3 set screw)",
   "fit": "slide",
   "files": "hub-"
  },
  {
   "feature": "hub set-screw hole",
   "exact": "Ø2.5",
   "mates": "M3 tap drill",
   "fit": "designed",
   "files": "hub-"
  }
 ],
 "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": "What is the hole in a CD?",
   "a": "Ø15; the CD hubs here have a Ø15 spigot 1.3 tall to match it."
  },
  {
   "q": "Which hub goes on a bamboo skewer?",
   "a": "Hub-cd-15-to-3: Ø3 bore, Ø15 spigot, M3 set screw."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "hub-cd-15-to-3",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/can-engine-printed-kit/hub-cd-15-to-3.step",
   "stl": "https://xemstudio.com/files/hardware/can-engine-printed-kit/hub-cd-15-to-3.stl",
   "note": "CD / DVD hub: Ø23 × 10 boss with a Ø3 shaft bore and M3 set-screw hole (Ø2.5), Ø15 × 1.2 spigot that takes the disc"
  },
  {
   "file": "hub-cd-15-to-5",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/can-engine-printed-kit/hub-cd-15-to-5.step",
   "stl": "https://xemstudio.com/files/hardware/can-engine-printed-kit/hub-cd-15-to-5.stl",
   "note": "CD / DVD hub: Ø23 × 10 boss with a Ø5 shaft bore and M3 set-screw hole (Ø2.5), Ø15 × 1.2 spigot that takes the disc"
  },
  {
   "file": "hub-cd-15-to-8",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/can-engine-printed-kit/hub-cd-15-to-8.step",
   "stl": "https://xemstudio.com/files/hardware/can-engine-printed-kit/hub-cd-15-to-8.stl",
   "note": "CD / DVD hub: Ø23 × 10 boss with a Ø8 shaft bore and M3 set-screw hole (Ø2.5), Ø15 × 1.2 spigot that takes the disc"
  },
  {
   "file": "hub-platter-25-to-8",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/can-engine-printed-kit/hub-platter-25-to-8.step",
   "stl": "https://xemstudio.com/files/hardware/can-engine-printed-kit/hub-platter-25-to-8.stl",
   "note": "3.5 in HDD platter hub: Ø33 × 10 boss with a Ø8 shaft bore and M3 set-screw hole (Ø2.5), Ø25 × 1.27 spigot that takes the platter"
  },
  {
   "file": "hub-platter-25-to-5",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/can-engine-printed-kit/hub-platter-25-to-5.step",
   "stl": "https://xemstudio.com/files/hardware/can-engine-printed-kit/hub-platter-25-to-5.stl",
   "note": "3.5 in HDD platter hub: Ø33 × 10 boss with a Ø5 shaft bore and M3 set-screw hole (Ø2.5), Ø25 × 1.27 spigot that takes the platter"
  }
 ],
 "markdown": "https://xemstudio.com/objects/flywheel-disc-hub/index.md"
}