{
 "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": "tri-clamp-flexure-ring",
 "name": "Flexure ring for the displacer stack: Ø76, Ø96 and Ø116 with Ø60, Ø80 and Ø100 seats",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Free-piston",
 "year": null,
 "question": "What holds the displacer's flexure stack above a free-piston head?",
 "tags": [
  "free piston",
  "flexure",
  "ring",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "flexure stack ring",
  "free piston displacer flexure mount",
  "flexure ring 80mm"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": true,
 "free_files": 3,
 "url": "https://xemstudio.com/objects/tri-clamp-flexure-ring/",
 "sheet_txt": "https://xemstudio.com/objects/tri-clamp-flexure-ring/sheet.txt",
 "sheet": {
  "basis": "Ring Ø = flexure OD + 16, 4 mm thick, flexure-OD × 1 seat, 3 × Ø3.4 on the 0.88 × OD circle (same as the flexure head)",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "The ring that carries the displacer's flexure stack (stack B) on three M3 standoffs above the flexure head.",
   "Ø76 / Ø96 / Ø116 × 4 mm for Ø60 / Ø80 / Ø100 leaves, with a seat the flexure OD × 1 mm deep, a centre window hub + 6 (Ø19.2 / Ø23.6 / Ø28), and three Ø3.4 holes on the same circle as the head (Ø52.8 / Ø70.4 / Ø88)."
  ],
  "table": {
   "columns": [
    "flexure_od_mm",
    "ring_od_mm",
    "thickness_mm",
    "seat_mm",
    "window_mm",
    "hole_circle_mm"
   ],
   "rows": [
    [
     60,
     76,
     4,
     "Ø60 × 1",
     19.2,
     52.8
    ],
    [
     80,
     96,
     4,
     "Ø80 × 1",
     23.6,
     70.4
    ],
    [
     100,
     116,
     4,
     "Ø100 × 1",
     28,
     88
    ]
   ]
  }
 },
 "sheet_text": "Flexure ring for the displacer stack: Ø76, Ø96 and Ø116 with Ø60, Ø80 and Ø100 seats — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/tri-clamp-flexure-ring/  (CC BY 4.0)\nBasis: Ring Ø = flexure OD + 16, 4 mm thick, flexure-OD × 1 seat, 3 × Ø3.4 on the 0.88 × OD circle (same as the flexure head)\nCatalog version: 2026-10-20\n\nSizes: see table below\n- The ring that carries the displacer's flexure stack (stack B) on three M3 standoffs above the flexure head.\n- Ø76 / Ø96 / Ø116 × 4 mm for Ø60 / Ø80 / Ø100 leaves, with a seat the flexure OD × 1 mm deep, a centre window hub + 6 (Ø19.2 / Ø23.6 / Ø28), and three Ø3.4 holes on the same circle as the head (Ø52.8 / Ø70.4 / Ø88).\n\nflexure_od_mm  ring_od_mm  thickness_mm  seat_mm  window_mm  hole_circle_mm\n60  76  4  Ø60 × 1  19.2  52.8\n80  96  4  Ø80 × 1  23.6  70.4\n100  116  4  Ø100 × 1  28.0  88.0\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, 3 parts): https://xemstudio.com/files/hardware/tri-clamp-flexure-ring/index.json\nAPI: https://xemstudio.com/api/geometry?object=tri-clamp-flexure-ring\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": [
  "tri-clamp-flexure-head",
  "spiral-flexure-bearing",
  "threaded-standoffs-metric",
  "flexure-hub-collar"
 ],
 "fits": [
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "tri-clamp-flexure-head",
     "why": "3 × M3 standoffs on the shared hole circle"
    },
    {
     "slug": "spiral-flexure-bearing",
     "why": "leaf rim in the seat"
    }
   ]
  },
  {
   "role": "Also needed",
   "items": [
    {
     "slug": "threaded-standoffs-metric",
     "why": "M3 standoffs"
    }
   ]
  }
 ],
 "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": "flexure pocket in the head / ring",
   "exact": "flexure OD",
   "mates": "spiral flexure leaf rim",
   "fit": "slide",
   "files": "fp-flexure-"
  },
  {
   "feature": "rim holes (head, ring)",
   "exact": "Ø3.4",
   "mates": "M3 screw clearance",
   "fit": "designed",
   "files": "fp-flexure-"
  },
  {
   "feature": "head / ring window",
   "exact": "hub + 12 (Ø29.6 on Ø80)",
   "mates": "hub collars and their pinch-screw heads (no contact)",
   "fit": "designed",
   "files": "fp-flexure-"
  }
 ],
 "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 far is the flexure ring above the head?",
   "a": "Set by the M3 standoffs between them; the stack-B height sets the displacer's moving mass and phase."
  },
  {
   "q": "Which ring goes with the 2 inch head?",
   "a": "Fp-flexure-ring-80: Ø96 × 4 with the Ø80 seat."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "fp-flexure-ring-60",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/fp-flexure-ring-60.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/fp-flexure-ring-60.stl",
   "note": "Ø76 × 4 ring for stack B (displacer rod) on 3 × M3 standoffs above the head: Ø60 × 1 flexure pocket, Ø25.2 window, 3 × Ø3.4"
  },
  {
   "file": "fp-flexure-ring-80",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/fp-flexure-ring-80.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/fp-flexure-ring-80.stl",
   "note": "Ø96 × 4 ring for stack B (displacer rod) on 3 × M3 standoffs above the head: Ø80 × 1 flexure pocket, Ø29.6 window, 3 × Ø3.4"
  },
  {
   "file": "fp-flexure-ring-100",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/fp-flexure-ring-100.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/fp-flexure-ring-100.stl",
   "note": "Ø116 × 4 ring for stack B (displacer rod) on 3 × M3 standoffs above the head: Ø100 × 1 flexure pocket, Ø34 window, 3 × Ø3.4"
  }
 ],
 "markdown": "https://xemstudio.com/objects/tri-clamp-flexure-ring/index.md"
}