{
 "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-stack-spacer",
 "name": "Flexure stack spacer ring: Ø40 to Ø120 × 2 mm",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Free-piston",
 "year": null,
 "question": "What spaces the leaves in a flexure bearing stack?",
 "tags": [
  "flexure",
  "spacer",
  "ring",
  "free piston",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "flexure spacer ring",
  "flexure stack spacer",
  "80mm spacer ring 2mm"
 ],
 "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-stack-spacer/",
 "sheet_txt": "https://xemstudio.com/objects/flexure-stack-spacer/sheet.txt",
 "sheet": {
  "basis": "Ring = the flexure rim: OD × (OD − 2 × 0.12 OD), 2 mm thick",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "A plain ring the size of a flexure leaf's rim, 2 mm thick, that sits between leaf rims so the arms can flex without touching.",
   "Ø40 × 4.8 wide, Ø60 × 7.2, Ø80 × 9.6, Ø100 × 12, Ø120 × 14.4; all 2.0 mm thick, with no rim holes."
  ],
  "table": {
   "columns": [
    "od_mm",
    "id_mm",
    "width_mm",
    "thickness_mm"
   ],
   "rows": [
    [
     40,
     30.4,
     4.8,
     2
    ],
    [
     60,
     45.6,
     7.2,
     2
    ],
    [
     80,
     60.8,
     9.6,
     2
    ],
    [
     100,
     76,
     12,
     2
    ],
    [
     120,
     91.2,
     14.4,
     2
    ]
   ]
  }
 },
 "sheet_text": "Flexure stack spacer ring: Ø40 to Ø120 × 2 mm — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/flexure-stack-spacer/  (CC BY 4.0)\nBasis: Ring = the flexure rim: OD × (OD − 2 × 0.12 OD), 2 mm thick\nCatalog version: 2026-10-20\n\nSizes: see table below\n- A plain ring the size of a flexure leaf's rim, 2 mm thick, that sits between leaf rims so the arms can flex without touching.\n- Ø40 × 4.8 wide, Ø60 × 7.2, Ø80 × 9.6, Ø100 × 12, Ø120 × 14.4; all 2.0 mm thick, with no rim holes.\n\nod_mm  id_mm  width_mm  thickness_mm\n40  30.4  4.8  2\n60  45.6  7.2  2\n80  60.8  9.6  2\n100  76  12  2\n120  91.2  14.4  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-stack-spacer/index.json\nAPI: https://xemstudio.com/api/geometry?object=flexure-stack-spacer\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-rim-clamp-plate",
  "flexure-hub-clamp-washer"
 ],
 "fits": [
  {
   "role": "Goes in or on",
   "items": [
    {
     "slug": "spiral-flexure-bearing",
     "why": "between leaf rims, same OD"
    }
   ]
  },
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "flexure-rim-clamp-plate",
     "why": "stack clamped under the plate"
    }
   ]
  },
  {
   "role": "Also needed",
   "items": [
    {
     "slug": "flexure-hub-clamp-washer",
     "why": "matching gap at the hubs"
    }
   ]
  }
 ],
 "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": "spacer rim holes",
   "exact": "Ø3.4 × 3 on R = 0.44·OD (R35.2 on Ø80)",
   "mates": "M3 stack screws (clearance)",
   "fit": "designed",
   "files": "spacer-"
  }
 ],
 "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 thick are the flexure stack spacers?",
   "a": "2.0 mm, the width of the leaf rim (9.6 mm on Ø80)."
  },
  {
   "q": "What size spacer goes with an Ø80 flexure?",
   "a": "Spacer-80-t2: Ø80 OD × Ø60.8 ID × 2.0 mm."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "spacer-40-t2",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/spiral-flexure-bearings/spacer-40-t2.step",
   "stl": "https://xemstudio.com/files/hardware/spiral-flexure-bearings/spacer-40-t2.stl",
   "note": "stack spacer ring Ø40, 4.8 wide, 2 thick (sets the gap between leaves), 3 × Ø3.4 on R17.6 (the leaves' rim-hole circle) for the stack screws"
  },
  {
   "file": "spacer-60-t2",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/spiral-flexure-bearings/spacer-60-t2.step",
   "stl": "https://xemstudio.com/files/hardware/spiral-flexure-bearings/spacer-60-t2.stl",
   "note": "stack spacer ring Ø60, 7.2 wide, 2 thick (sets the gap between leaves), 3 × Ø3.4 on R26.4 (the leaves' rim-hole circle) for the stack screws"
  },
  {
   "file": "spacer-80-t2",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/spiral-flexure-bearings/spacer-80-t2.step",
   "stl": "https://xemstudio.com/files/hardware/spiral-flexure-bearings/spacer-80-t2.stl",
   "note": "stack spacer ring Ø80, 9.6 wide, 2 thick (sets the gap between leaves), 3 × Ø3.4 on R35.2 (the leaves' rim-hole circle) for the stack screws"
  },
  {
   "file": "spacer-100-t2",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/spiral-flexure-bearings/spacer-100-t2.step",
   "stl": "https://xemstudio.com/files/hardware/spiral-flexure-bearings/spacer-100-t2.stl",
   "note": "stack spacer ring Ø100, 12 wide, 2 thick (sets the gap between leaves), 3 × Ø3.4 on R44 (the leaves' rim-hole circle) for the stack screws"
  },
  {
   "file": "spacer-120-t2",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/spiral-flexure-bearings/spacer-120-t2.step",
   "stl": "https://xemstudio.com/files/hardware/spiral-flexure-bearings/spacer-120-t2.stl",
   "note": "stack spacer ring Ø120, 14.4 wide, 2 thick (sets the gap between leaves), 3 × Ø3.4 on R52.8 (the leaves' rim-hole circle) for the stack screws"
  }
 ],
 "markdown": "https://xemstudio.com/objects/flexure-stack-spacer/index.md"
}