{
 "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": "flexure-hub-centring-bush",
 "name": "Flexure hub centring bush: Ø5 and Ø8 OD × Ø3 / Ø5 bore × 6",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Free-piston",
 "year": null,
 "question": "How do I centre a flexure with a 5 mm hub hole on a 3 mm rod?",
 "tags": [
  "flexure",
  "bush",
  "sleeve",
  "free piston",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "flexure centring bush",
  "5mm to 3mm sleeve",
  "8mm to 5mm sleeve",
  "flexure hub adapter"
 ],
 "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/flexure-hub-centring-bush/",
 "sheet_txt": "https://xemstudio.com/objects/flexure-hub-centring-bush/sheet.txt",
 "sheet": {
  "basis": "OD = flexure leaf hub bore (Ø5 for Ø60/Ø80 leaves, Ø8 for Ø100), ID = rod or tube, 6 long = two 2 mm leaf hubs and the 2 mm hub washer between them",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "A plain sleeve that centres flexure leaves whose hub hole is bigger than the rod: the two leaf hubs and the hub washer between them sit on its OD, the rod runs through its bore, and the two hub collars (bore = rod) clamp its ends.",
   "Hub-bush-60-b3 and hub-bush-80-b3: Ø5 OD × Ø3 bore × 6 for Ø60 / Ø80 leaves on the Ø3 displacer rod. hub-bush-100-b3: Ø8 × Ø3 × 6. hub-bush-100-b5: Ø8 × Ø5 × 6 for Ø100 leaves on the 5 mm tube piston rod."
  ],
  "table": {
   "columns": [
    "file",
    "od_mm",
    "bore_mm",
    "length_mm",
    "for"
   ],
   "rows": [
    [
     "hub-bush-60-b3",
     5,
     3,
     6,
     "Ø60 leaves, Ø3 rod"
    ],
    [
     "hub-bush-80-b3",
     5,
     3,
     6,
     "Ø80 leaves, Ø3 rod"
    ],
    [
     "hub-bush-100-b3",
     8,
     3,
     6,
     "Ø100 leaves, Ø3 rod"
    ],
    [
     "hub-bush-100-b5",
     8,
     5,
     6,
     "Ø100 leaves, 5 mm tube"
    ]
   ]
  }
 },
 "sheet_text": "Flexure hub centring bush: Ø5 and Ø8 OD × Ø3 / Ø5 bore × 6 — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/flexure-hub-centring-bush/  (CC BY 4.0)\nBasis: OD = flexure leaf hub bore (Ø5 for Ø60/Ø80 leaves, Ø8 for Ø100), ID = rod or tube, 6 long = two 2 mm leaf hubs and the 2 mm hub washer between them\nCatalog version: 2026-10-20\n\nSizes: see table below\n- A plain sleeve that centres flexure leaves whose hub hole is bigger than the rod: the two leaf hubs and the hub washer between them sit on its OD, the rod runs through its bore, and the two hub collars (bore = rod) clamp its ends.\n- Hub-bush-60-b3 and hub-bush-80-b3: Ø5 OD × Ø3 bore × 6 for Ø60 / Ø80 leaves on the Ø3 displacer rod. hub-bush-100-b3: Ø8 × Ø3 × 6. hub-bush-100-b5: Ø8 × Ø5 × 6 for Ø100 leaves on the 5 mm tube piston rod.\n\nfile  od_mm  bore_mm  length_mm  for\nhub-bush-60-b3  5  3  6  Ø60 leaves, Ø3 rod\nhub-bush-80-b3  5  3  6  Ø80 leaves, Ø3 rod\nhub-bush-100-b3  8  3  6  Ø100 leaves, Ø3 rod\nhub-bush-100-b5  8  5  6  Ø100 leaves, 5 mm tube\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- NASA NTRS: Free-piston Stirling convertor flexure bearing development and life testing — pdf — US Government work — https://ntrs.nasa.gov/citations/20050182933\n- Long Earth Society: Tri-clamp Stirling engine builds — web, video — LES site — https://longearthsociety.com/engineering/\n- Wikipedia: Free-piston engine — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Free-piston_engine\n\nFree files (CC BY 4.0, Xem Studio; STEP + STL, 4 parts): https://xemstudio.com/files/hardware/flexure-hub-centring-bush/index.json\nAPI: https://xemstudio.com/api/geometry?object=flexure-hub-centring-bush\n",
 "sources": [
  {
   "publisher": "NASA NTRS",
   "title": "Free-piston Stirling convertor flexure bearing development and life testing",
   "url": "https://ntrs.nasa.gov/citations/20050182933",
   "formats": [
    "pdf"
   ],
   "license": "US Government work",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Long Earth Society",
   "title": "Tri-clamp Stirling engine builds",
   "url": "https://longearthsociety.com/engineering/",
   "formats": [
    "web",
    "video"
   ],
   "license": "LES site",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Wikipedia",
   "title": "Free-piston engine",
   "url": "https://en.wikipedia.org/wiki/Free-piston_engine",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text)",
   "license_verified": true,
   "hosted": false
  }
 ],
 "xem": {
  "status": "free-files",
  "sheet_free": true,
  "mesh_price_usd": null,
  "step_price_usd": null,
  "tolerance_mm": null
 },
 "related": [
  "spiral-flexure-bearing",
  "flexure-hub-collar",
  "stirling-crankshafts"
 ],
 "fits": [
  {
   "role": "Goes in or on",
   "items": [
    {
     "slug": "spiral-flexure-bearing",
     "why": "OD = leaf hub bore"
    }
   ]
  },
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "stirling-crankshafts",
     "why": "Ø3 displacer rod or 5 mm tube in the bore"
    }
   ]
  },
  {
   "role": "Also needed",
   "items": [
    {
     "slug": "flexure-hub-collar",
     "why": "collars clamp the stack ends"
    }
   ]
  }
 ],
 "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": "centring bush OD",
   "exact": "leaf hub bore (Ø5 / Ø8)",
   "mates": "flexure leaf hub",
   "fit": "slide",
   "files": "hub-bush-"
  },
  {
   "feature": "centring bush bore",
   "exact": "Ø3 / Ø5",
   "mates": "Ø3 rod / 5 mm tube",
   "fit": "slide",
   "files": "hub-bush-"
  }
 ],
 "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 do I fit a 5 mm flexure hub on a 3 mm rod?",
   "a": "On the Ø5 × Ø3 × 6 centring bush: the two leaf hubs and the hub washer sit on its OD, the rod passes its bore, and hub collars clamp the ends."
  },
  {
   "q": "Why is there a b5 bush only for Ø100?",
   "a": "The Ø60 and Ø80 leaves already have a Ø5 hub bore for the 5 mm tube; only the Ø100 leaves (Ø8 hub bore) need a Ø8 × Ø5 bush."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "hub-bush-60-b3",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/hub-bush-60-b3.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/hub-bush-60-b3.stl",
   "note": "centring bush Ø5 OD × Ø3 ID × 6: fills the two leaf hubs and the hub washer (Ø5 bores) and centres them on the Ø3 displacer rod; the b3 collars clamp its ends"
  },
  {
   "file": "hub-bush-80-b3",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/hub-bush-80-b3.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/hub-bush-80-b3.stl",
   "note": "centring bush Ø5 OD × Ø3 ID × 6: fills the two leaf hubs and the hub washer (Ø5 bores) and centres them on the Ø3 displacer rod; the b3 collars clamp its ends"
  },
  {
   "file": "hub-bush-100-b3",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/hub-bush-100-b3.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/hub-bush-100-b3.stl",
   "note": "centring bush Ø8 OD × Ø3 ID × 6: fills the two leaf hubs and the hub washer (Ø8 bores) and centres them on the Ø3 displacer rod; the b3 collars clamp its ends"
  },
  {
   "file": "hub-bush-100-b5",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/hub-bush-100-b5.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/hub-bush-100-b5.stl",
   "note": "centring bush Ø8 × Ø5 × 6: centres the Ø100 leaves and hub washer on the 5 mm tube piston rod"
  }
 ],
 "markdown": "https://xemstudio.com/objects/flexure-hub-centring-bush/index.md"
}