{
 "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-clamp-washer",
 "name": "Flexure hub washer: Ø12 to Ø26.4 × 2 mm",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Free-piston",
 "year": null,
 "question": "What goes between the hubs in a flexure bearing stack?",
 "tags": [
  "flexure",
  "washer",
  "hub",
  "free piston",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "flexure hub washer",
  "flexure hub spacer",
  "flexure stack washer"
 ],
 "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/flexure-hub-clamp-washer/",
 "sheet_txt": "https://xemstudio.com/objects/flexure-hub-clamp-washer/sheet.txt",
 "sheet": {
  "basis": "Washer = the leaf hub: Ø hub × leaf bore, 2 mm thick, the same as the rim spacer",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "A 2 mm washer the size of a leaf's hub, with the leaf's bore, that sits between the two leaf hubs of a stack: as thick as the 2 mm rim spacer between the leaf rims, so both leaves stay flat and parallel.",
   "Ø12 × Ø4, Ø13.2 × Ø5, Ø17.6 × Ø5, Ø22 × Ø8, Ø26.4 × Ø8 for the Ø40 to Ø120 leaves."
  ],
  "table": {
   "columns": [
    "flexure_od_mm",
    "od_mm",
    "bore_mm",
    "thickness_mm"
   ],
   "rows": [
    [
     40,
     12,
     4,
     2
    ],
    [
     60,
     13.2,
     5,
     2
    ],
    [
     80,
     17.6,
     5,
     2
    ],
    [
     100,
     22,
     8,
     2
    ],
    [
     120,
     26.4,
     8,
     2
    ]
   ]
  }
 },
 "sheet_text": "Flexure hub washer: Ø12 to Ø26.4 × 2 mm — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/flexure-hub-clamp-washer/  (CC BY 4.0)\nBasis: Washer = the leaf hub: Ø hub × leaf bore, 2 mm thick, the same as the rim spacer\nCatalog version: 2026-10-20\n\nSizes: see table below\n- A 2 mm washer the size of a leaf's hub, with the leaf's bore, that sits between the two leaf hubs of a stack: as thick as the 2 mm rim spacer between the leaf rims, so both leaves stay flat and parallel.\n- Ø12 × Ø4, Ø13.2 × Ø5, Ø17.6 × Ø5, Ø22 × Ø8, Ø26.4 × Ø8 for the Ø40 to Ø120 leaves.\n\nflexure_od_mm  od_mm  bore_mm  thickness_mm\n40  12  4  2\n60  13.2  5  2\n80  17.6  5  2\n100  22  8  2\n120  26.4  8  2\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- NASA (NTRS, public domain): Free-piston Stirling convertor flexure bearing development and life testing (2005) — PDF — US Government work, public domain — https://ntrs.nasa.gov/search?q=20050182933\n- NASA (NTRS, public domain): Flexure bearing design for free-piston Stirling engines (1986) — PDF — US Government work, public domain — https://ntrs.nasa.gov/search?q=19860020334\n- NASA (NTRS, public domain): Advanced Stirling Radioisotope Generator (ASRG) engineering unit (2011) — PDF — US Government work, public domain — https://ntrs.nasa.gov/search?q=20110016393\n- Wikipedia: Flexure bearing — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Flexure_bearing\n- Sunpower (AMETEK): Free-piston Stirling technology overview — web — Sunpower site [verify license at link] — https://sunpowerinc.com/\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, 5 parts): https://xemstudio.com/files/hardware/flexure-hub-clamp-washer/index.json\nAPI: https://xemstudio.com/api/geometry?object=flexure-hub-clamp-washer\n",
 "sources": [
  {
   "publisher": "NASA (NTRS, public domain)",
   "title": "Free-piston Stirling convertor flexure bearing development and life testing (2005)",
   "url": "https://ntrs.nasa.gov/search?q=20050182933",
   "formats": [
    "PDF"
   ],
   "license": "US Government work, public domain",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "NASA (NTRS, public domain)",
   "title": "Flexure bearing design for free-piston Stirling engines (1986)",
   "url": "https://ntrs.nasa.gov/search?q=19860020334",
   "formats": [
    "PDF"
   ],
   "license": "US Government work, public domain",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "NASA (NTRS, public domain)",
   "title": "Advanced Stirling Radioisotope Generator (ASRG) engineering unit (2011)",
   "url": "https://ntrs.nasa.gov/search?q=20110016393",
   "formats": [
    "PDF"
   ],
   "license": "US Government work, public domain",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Wikipedia",
   "title": "Flexure bearing",
   "url": "https://en.wikipedia.org/wiki/Flexure_bearing",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text)",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Sunpower (AMETEK)",
   "title": "Free-piston Stirling technology overview",
   "url": "https://sunpowerinc.com/",
   "formats": [
    "web"
   ],
   "license": "Sunpower site",
   "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": [
  "spiral-flexure-bearing",
  "flexure-hub-collar",
  "flexure-hub-centring-bush",
  "flexure-stack-spacer"
 ],
 "fits": [
  {
   "role": "Goes in or on",
   "items": [
    {
     "slug": "spiral-flexure-bearing",
     "why": "between leaf hubs, same bore"
    }
   ]
  },
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "flexure-hub-collar",
     "why": "collars clamp the hub stack"
    },
    {
     "slug": "flexure-hub-centring-bush",
     "why": "rides on the bush when the rod is smaller than the bore"
    }
   ]
  }
 ],
 "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-clamp bore",
   "exact": "Ø4 / Ø5 / Ø8",
   "mates": "rod, tube or centring bush",
   "fit": "slide",
   "files": "hub-clamp-"
  },
  {
   "feature": "hub washer thickness",
   "exact": "2 (= rim spacer)",
   "mates": "the two leaf hubs either side",
   "fit": "designed",
   "files": "hub-clamp-"
  }
 ],
 "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 size is the hub washer for an Ø80 flexure?",
   "a": "Ø17.6 × Ø5 bore × 2 mm, the same thickness as the rim spacer."
  },
  {
   "q": "Which hub washer goes with which leaf?",
   "a": "The one with the same OD: Ø12 for Ø40 leaves, Ø13.2 for Ø60, Ø17.6 for Ø80, Ø22 for Ø100, Ø26.4 for Ø120, each with that leaf's bore."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "hub-clamp-40-b4",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/spiral-flexure-bearings/hub-clamp-40-b4.step",
   "stl": "https://xemstudio.com/files/hardware/spiral-flexure-bearings/hub-clamp-40-b4.stl",
   "note": "hub washer Ø12, Ø4 bore, 2 thick (= the rim spacer): between the two leaf hubs of a stack"
  },
  {
   "file": "hub-clamp-60-b5",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/spiral-flexure-bearings/hub-clamp-60-b5.step",
   "stl": "https://xemstudio.com/files/hardware/spiral-flexure-bearings/hub-clamp-60-b5.stl",
   "note": "hub washer Ø13.2, Ø5 bore, 2 thick (= the rim spacer): between the two leaf hubs of a stack"
  },
  {
   "file": "hub-clamp-80-b5",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/spiral-flexure-bearings/hub-clamp-80-b5.step",
   "stl": "https://xemstudio.com/files/hardware/spiral-flexure-bearings/hub-clamp-80-b5.stl",
   "note": "hub washer Ø17.6, Ø5 bore, 2 thick (= the rim spacer): between the two leaf hubs of a stack"
  },
  {
   "file": "hub-clamp-100-b8",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/spiral-flexure-bearings/hub-clamp-100-b8.step",
   "stl": "https://xemstudio.com/files/hardware/spiral-flexure-bearings/hub-clamp-100-b8.stl",
   "note": "hub washer Ø22, Ø8 bore, 2 thick (= the rim spacer): between the two leaf hubs of a stack"
  },
  {
   "file": "hub-clamp-120-b8",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/spiral-flexure-bearings/hub-clamp-120-b8.step",
   "stl": "https://xemstudio.com/files/hardware/spiral-flexure-bearings/hub-clamp-120-b8.stl",
   "note": "hub washer Ø26.4, Ø8 bore, 2 thick (= the rim spacer): between the two leaf hubs of a stack"
  }
 ],
 "markdown": "https://xemstudio.com/objects/flexure-hub-clamp-washer/index.md"
}