{
 "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": "cd-dvd-and-drive-platters",
 "name": "CDs, DVDs and hard-drive platters as flywheels",
 "kind": "standard",
 "category": "Hardware",
 "group": "Found & household materials",
 "year": null,
 "question": "What are the dimensions of a CD and its centre hole?",
 "tags": [
  "cd",
  "dvd",
  "platter",
  "flywheel",
  "disc",
  "stirling",
  "long earth society",
  "found materials"
 ],
 "aliases": [
  "cd dimensions",
  "cd center hole size",
  "dvd diameter mm",
  "hard drive platter dimensions",
  "cd flywheel",
  "hdd platter hole size",
  "cd stirling engine flywheel"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": true,
 "free_files": 4,
 "url": "https://xemstudio.com/objects/cd-dvd-and-drive-platters/",
 "sheet_txt": "https://xemstudio.com/objects/cd-dvd-and-drive-platters/sheet.txt",
 "sheet": {
  "basis": "ECMA-130 / ISO 9660 physical disc: Ø120 × 1.2 mm, Ø15 mm hole; hard-drive platters per the 3.5 in (95 mm) and 2.5 in (65 mm) form factors",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "CD/DVD/Blu-ray: Ø120.0 mm, 1.2 mm thick, Ø15.0 mm centre hole, 16 g polycarbonate. Mini CD Ø80. The hole is held to +0.1 mm, so a printed Ø14.9 hub press-fits.",
   "3.5 in drive platter: Ø95 × 1.27 mm (some 0.8–1.0), Ø25 mm hole, aluminium (older, 30 g) or glass (newer, do not drill). 2.5 in platter: Ø65 × 0.8, Ø20 hole. Mirror-flat, perfectly balanced: a stack of three 3.5 in platters on the printed hub is a 90 g, Ø95 flywheel.",
   "The hubs in the can-engine kit take a CD (Ø15 bore) or a 3.5 in platter (Ø25) onto a 5 mm or 8 mm shaft with a set screw. Two CDs glued with a 1 mm spacer are stiffer than one.",
   "A CD flywheel is 16 g at Ø120: it stores as much energy as a Ø60 × 10 mm steel disc, which is why the can engine runs on it."
  ],
  "table": {
   "columns": [
    "disc",
    "dia_mm",
    "thickness_mm",
    "hole_mm",
    "mass_g"
   ],
   "rows": [
    [
     "CD / DVD",
     120,
     1.2,
     15,
     16
    ],
    [
     "mini CD",
     80,
     1.2,
     15,
     7
    ],
    [
     "3.5 in HDD platter",
     95,
     1.27,
     25,
     30
    ],
    [
     "2.5 in HDD platter",
     65,
     0.8,
     20,
     7
    ]
   ]
  }
 },
 "sheet_text": "CDs, DVDs and hard-drive platters as flywheels — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/cd-dvd-and-drive-platters/  (CC BY 4.0)\nBasis: ECMA-130 / ISO 9660 physical disc: Ø120 × 1.2 mm, Ø15 mm hole; hard-drive platters per the 3.5 in (95 mm) and 2.5 in (65 mm) form factors\nCatalog version: 2026-10-20\n\nSizes: see table below\n- CD/DVD/Blu-ray: Ø120.0 mm, 1.2 mm thick, Ø15.0 mm centre hole, 16 g polycarbonate. Mini CD Ø80. The hole is held to +0.1 mm, so a printed Ø14.9 hub press-fits.\n- 3.5 in drive platter: Ø95 × 1.27 mm (some 0.8–1.0), Ø25 mm hole, aluminium (older, 30 g) or glass (newer, do not drill). 2.5 in platter: Ø65 × 0.8, Ø20 hole. Mirror-flat, perfectly balanced: a stack of three 3.5 in platters on the printed hub is a 90 g, Ø95 flywheel.\n- The hubs in the can-engine kit take a CD (Ø15 bore) or a 3.5 in platter (Ø25) onto a 5 mm or 8 mm shaft with a set screw. Two CDs glued with a 1 mm spacer are stiffer than one.\n- A CD flywheel is 16 g at Ø120: it stores as much energy as a Ø60 × 10 mm steel disc, which is why the can engine runs on it.\n\ndisc  dia_mm  thickness_mm  hole_mm  mass_g\nCD / DVD  120  1.2  15  16\nmini CD  80  1.2  15  7\n3.5 in HDD platter  95  1.27  25  30\n2.5 in HDD platter  65  0.8  20  7\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Wikipedia: Compact disc — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Compact_disc\n- Wikipedia: Hard disk drive platter — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Hard_disk_drive_platter\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, 4 parts): https://xemstudio.com/files/hardware/cd-dvd-and-drive-platters/index.json\nAPI: https://xemstudio.com/api/geometry?object=cd-dvd-and-drive-platters\n",
 "sources": [
  {
   "publisher": "Wikipedia",
   "title": "Compact disc",
   "url": "https://en.wikipedia.org/wiki/Compact_disc",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text)",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Wikipedia",
   "title": "Hard disk drive platter",
   "url": "https://en.wikipedia.org/wiki/Hard_disk_drive_platter",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text)",
   "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": [
  "can-engine-printed-kit",
  "crank-conrod-flywheel-kit",
  "ball-bearings-metric",
  "beverage-cans"
 ],
 "faq": [
  {
   "q": "What is the diameter of a CD centre hole?",
   "a": "15.0 mm (+0.1); the disc is Ø120 × 1.2 mm. A printed Ø14.9 mm hub press-fits."
  },
  {
   "q": "What are hard drive platter dimensions?",
   "a": "3.5 in drives: Ø95 mm, 25 mm hole, about 1.27 mm thick (aluminium) or 0.8–1.0 (glass). 2.5 in drives: Ø65, 20 mm hole, 0.8 mm."
  },
  {
   "q": "Is a CD a good flywheel?",
   "a": "For a can or test-tube Stirling, yes: 16 g at Ø120 mm beats a small solid disc; stack two for stiffness and glue a coin at the rim to balance."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "cd-dvd-120",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/cd-dvd-and-drive-platters/cd-dvd-120.step",
   "stl": "https://xemstudio.com/files/hardware/cd-dvd-and-drive-platters/cd-dvd-120.stl",
   "note": "CD / DVD / Blu-ray: Ø120 × 1.2, Ø15 hole (Ø15.0 +0.1)"
  },
  {
   "file": "mini-cd-80",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/cd-dvd-and-drive-platters/mini-cd-80.step",
   "stl": "https://xemstudio.com/files/hardware/cd-dvd-and-drive-platters/mini-cd-80.stl",
   "note": "Mini CD: Ø80 × 1.2, Ø15 hole"
  },
  {
   "file": "hdd-platter-3-5in",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/cd-dvd-and-drive-platters/hdd-platter-3-5in.step",
   "stl": "https://xemstudio.com/files/hardware/cd-dvd-and-drive-platters/hdd-platter-3-5in.stl",
   "note": "3.5 in hard-drive platter: Ø95 × 1.27, Ø25 hole (aluminium or glass)"
  },
  {
   "file": "hdd-platter-2-5in",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/cd-dvd-and-drive-platters/hdd-platter-2-5in.step",
   "stl": "https://xemstudio.com/files/hardware/cd-dvd-and-drive-platters/hdd-platter-2-5in.stl",
   "note": "2.5 in platter: Ø65 × 0.8, Ø20 hole"
  }
 ],
 "markdown": "https://xemstudio.com/objects/cd-dvd-and-drive-platters/index.md"
}