{
 "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-head",
 "name": "Tri-clamp flexure head: ISO 2852 cap with Ø60, Ø80 and Ø100 flexure seats",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Free-piston",
 "year": null,
 "question": "How do I mount flexure bearings on a tri-clamp spool?",
 "tags": [
  "free piston",
  "flexure",
  "tri-clamp",
  "stirling",
  "head",
  "long earth society"
 ],
 "aliases": [
  "free piston stirling tri clamp",
  "flexure bearing mount stirling",
  "tri clamp flexure head",
  "fpse head"
 ],
 "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-head/",
 "sheet_txt": "https://xemstudio.com/objects/tri-clamp-flexure-head/sheet.txt",
 "sheet": {
  "basis": "ISO 2852 cap face; pedestal Ø = tube OD; plate Ø = flexure OD + 16 with a flexure-OD × 1 seat and 3 × Ø3.4 on the flexure rim-hole circle (0.88 × OD)",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "The head of the tri-clamp free-piston engine: it clamps on the spool's open ferrule and carries the piston's flexure stack (stack A).",
   "Base: 6 mm ISO 2852 cap, pedestal the tube's OD (38.1 / 50.8 / 76.2) to 14 mm so the clamp clears, then a plate 4 mm thick, Ø76 / Ø96 / Ø116. Overall 18 mm.",
   "On top: a seat Ø60 / Ø80 / Ø100 × 1 mm deep (the flexure OD) and three Ø3.4 holes on the flexure's rim-hole circle (Ø52.8 / Ø70.4 / Ø88). A centre window Ø19.2 / Ø23.6 / Ø28 (hub + 6) lets the rods through."
  ],
  "table": {
   "columns": [
    "spool_in",
    "flange_od_mm",
    "plate_od_mm",
    "flexure_seat_mm",
    "rim_hole_circle_mm",
    "window_mm",
    "height_mm"
   ],
   "rows": [
    [
     "1.5",
     50.5,
     76,
     "Ø60 × 1",
     52.8,
     19.2,
     18
    ],
    [
     "2",
     64,
     96,
     "Ø80 × 1",
     70.4,
     23.6,
     18
    ],
    [
     "3",
     91,
     116,
     "Ø100 × 1",
     88,
     28,
     18
    ]
   ]
  }
 },
 "sheet_text": "Tri-clamp flexure head: ISO 2852 cap with Ø60, Ø80 and Ø100 flexure seats — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/tri-clamp-flexure-head/  (CC BY 4.0)\nBasis: ISO 2852 cap face; pedestal Ø = tube OD; plate Ø = flexure OD + 16 with a flexure-OD × 1 seat and 3 × Ø3.4 on the flexure rim-hole circle (0.88 × OD)\nCatalog version: 2026-10-20\n\nSizes: see table below\n- The head of the tri-clamp free-piston engine: it clamps on the spool's open ferrule and carries the piston's flexure stack (stack A).\n- Base: 6 mm ISO 2852 cap, pedestal the tube's OD (38.1 / 50.8 / 76.2) to 14 mm so the clamp clears, then a plate 4 mm thick, Ø76 / Ø96 / Ø116. Overall 18 mm.\n- On top: a seat Ø60 / Ø80 / Ø100 × 1 mm deep (the flexure OD) and three Ø3.4 holes on the flexure's rim-hole circle (Ø52.8 / Ø70.4 / Ø88). A centre window Ø19.2 / Ø23.6 / Ø28 (hub + 6) lets the rods through.\n\nspool_in  flange_od_mm  plate_od_mm  flexure_seat_mm  rim_hole_circle_mm  window_mm  height_mm\n1.5  50.5  76  Ø60 × 1  52.8  19.2  18\n2  64.0  96  Ø80 × 1  70.4  23.6  18\n3  91.0  116  Ø100 × 1  88.0  28.0  18\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-head/index.json\nAPI: https://xemstudio.com/api/geometry?object=tri-clamp-flexure-head\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",
  "tri-clamp-flexure-ring",
  "flexure-hub-collar",
  "tri-clamp-piston-plug",
  "linear-alternator-mover",
  "tri-clamp-clamps"
 ],
 "fits": [
  {
   "role": "Parts that fit it",
   "items": [
    {
     "slug": "linear-alternator-housing",
     "why": "on standoffs on the flexure head's rim screws"
    },
    {
     "slug": "tube-piston-rods-5mm",
     "why": "Ø5 OD in the piston plug socket"
    }
   ]
  },
  {
   "role": "Goes in or on",
   "items": [
    {
     "slug": "tri-clamp-spool",
     "why": "ISO 2852 face on the open ferrule"
    }
   ]
  },
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "spiral-flexure-bearing",
     "why": "leaf rim in the flexure-OD seat, 3 × M3"
    },
    {
     "slug": "tri-clamp-flexure-ring",
     "why": "3 × M3 standoffs to the ring above"
    },
    {
     "slug": "linear-alternator-mover",
     "why": "alternator housing on the same three rim holes"
    }
   ]
  },
  {
   "role": "Also needed",
   "items": [
    {
     "slug": "tri-clamp-clamps",
     "why": "clamp and gasket on the face"
    }
   ]
  }
 ],
 "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": "head face",
   "exact": "ISO 2852",
   "mates": "ferrule face + Type B gasket",
   "fit": "clamp",
   "files": "fp-flexure-head-"
  },
  {
   "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": "What flexure size goes on a 2 inch tri-clamp spool?",
   "a": "Ø80 leaves on the 2 in flexure head (Ø96 plate); Ø60 on 1.5 in, Ø100 on 3 in."
  },
  {
   "q": "How are the flexures held on the head?",
   "a": "The leaf rim sits in the 1 mm deep seat and three M3 screws pass the Ø3.4 holes on the Ø70.4 circle (2 in) through the stack's spacers and clamp plate."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "fp-flexure-head-1.5in",
   "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-head-1.5in.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/fp-flexure-head-1.5in.stl",
   "note": "1.5 in flexure head: ISO 2852 cap face, Ø38.1 pedestal clearing the clamp, Ø76 plate with a Ø60 × 1 pocket (= flexure OD), a Ø25.2 window for the hub collars and 3 × M3 (Ø3.4) on the Ø60 flexure's rim holes; the piston's stack A bolts on it"
  },
  {
   "file": "fp-flexure-head-2in",
   "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-head-2in.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/fp-flexure-head-2in.stl",
   "note": "2 in flexure head: ISO 2852 cap face, Ø50.8 pedestal clearing the clamp, Ø96 plate with a Ø80 × 1 pocket (= flexure OD), a Ø29.6 window for the hub collars and 3 × M3 (Ø3.4) on the Ø80 flexure's rim holes; the piston's stack A bolts on it"
  },
  {
   "file": "fp-flexure-head-3in",
   "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-head-3in.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/fp-flexure-head-3in.stl",
   "note": "3 in flexure head: ISO 2852 cap face, Ø76.2 pedestal clearing the clamp, Ø116 plate with a Ø100 × 1 pocket (= flexure OD), a Ø34 window for the hub collars and 3 × M3 (Ø3.4) on the Ø100 flexure's rim holes; the piston's stack A bolts on it"
  }
 ],
 "markdown": "https://xemstudio.com/objects/tri-clamp-flexure-head/index.md"
}