{
 "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-collar",
 "name": "Flexure hub collars: split collars Ø13.2, Ø17.6 and Ø22 for Ø3 rod and Ø5 tube",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Free-piston",
 "year": null,
 "question": "How do I clamp a flexure leaf hub onto a piston rod?",
 "tags": [
  "flexure",
  "hub",
  "collar",
  "free piston",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "flexure hub clamp collar",
  "split collar 5mm",
  "split collar 3mm",
  "flexure stack collar"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": true,
 "free_files": 6,
 "url": "https://xemstudio.com/objects/flexure-hub-collar/",
 "sheet_txt": "https://xemstudio.com/objects/flexure-hub-collar/sheet.txt",
 "sheet": {
  "basis": "Collar Ø = flexure hub Ø (max(bore + 8, 0.22 × OD)); 6 mm thick so the M3 pinch screw's head (Ø5.5) stays within it; 0.8 mm slit; M3 pinch (Ø2.5)",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "A split clamping collar the size of a flexure leaf's hub: two per stack, one each end, squeeze the leaves, hub washers and spacers onto the rod.",
   "Ø13.2 (for Ø60 leaves), Ø17.6 (Ø80) and Ø22 (Ø100), all 6 mm thick. b5 collars have a Ø5 bore for the 5 mm tube piston rod; b3 collars a Ø3 bore for the displacer rod.",
   "A 0.8 mm slit runs from the bore to the rim, closed by an M3 × 10 screw in a Ø2.5 tangential hole at mid-thickness; the screw head stays inside the collar's 6 mm, clear of the leaf beside it."
  ],
  "table": {
   "columns": [
    "flexure_od_mm",
    "collar_od_mm",
    "bore_mm",
    "thickness_mm",
    "slit_mm",
    "pinch"
   ],
   "rows": [
    [
     60,
     13.2,
     "5 / 3",
     6,
     0.8,
     "M3 (Ø2.5)"
    ],
    [
     80,
     17.6,
     "5 / 3",
     6,
     0.8,
     "M3 (Ø2.5)"
    ],
    [
     100,
     22,
     "5 / 3",
     6,
     0.8,
     "M3 (Ø2.5)"
    ]
   ]
  }
 },
 "sheet_text": "Flexure hub collars: split collars Ø13.2, Ø17.6 and Ø22 for Ø3 rod and Ø5 tube — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/flexure-hub-collar/  (CC BY 4.0)\nBasis: Collar Ø = flexure hub Ø (max(bore + 8, 0.22 × OD)); 6 mm thick so the M3 pinch screw's head (Ø5.5) stays within it; 0.8 mm slit; M3 pinch (Ø2.5)\nCatalog version: 2026-10-20\n\nSizes: see table below\n- A split clamping collar the size of a flexure leaf's hub: two per stack, one each end, squeeze the leaves, hub washers and spacers onto the rod.\n- Ø13.2 (for Ø60 leaves), Ø17.6 (Ø80) and Ø22 (Ø100), all 6 mm thick. b5 collars have a Ø5 bore for the 5 mm tube piston rod; b3 collars a Ø3 bore for the displacer rod.\n- A 0.8 mm slit runs from the bore to the rim, closed by an M3 × 10 screw in a Ø2.5 tangential hole at mid-thickness; the screw head stays inside the collar's 6 mm, clear of the leaf beside it.\n\nflexure_od_mm  collar_od_mm  bore_mm  thickness_mm  slit_mm  pinch\n60  13.2  5 / 3  6  0.8  M3 (Ø2.5)\n80  17.6  5 / 3  6  0.8  M3 (Ø2.5)\n100  22.0  5 / 3  6  0.8  M3 (Ø2.5)\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, 6 parts): https://xemstudio.com/files/hardware/flexure-hub-collar/index.json\nAPI: https://xemstudio.com/api/geometry?object=flexure-hub-collar\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-centring-bush",
  "flexure-hub-clamp-washer",
  "tri-clamp-piston-plug"
 ],
 "fits": [
  {
   "role": "Goes in or on",
   "items": [
    {
     "slug": "spiral-flexure-bearing",
     "why": "one each end of the leaf stack on the hub"
    }
   ]
  },
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "tri-clamp-piston-plug",
     "why": "b5 collar on the 5 mm tube from the plug"
    },
    {
     "slug": "flexure-hub-centring-bush",
     "why": "collars clamp the stack on the bush"
    }
   ]
  },
  {
   "role": "Also needed",
   "items": [
    {
     "slug": "socket-head-cap-screws-metric",
     "why": "M3 pinch screw"
    }
   ]
  }
 ],
 "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 collar bore (b5 / b3)",
   "exact": "Ø5 / Ø3",
   "mates": "5 mm tube / Ø3 rod",
   "fit": "slide",
   "files": "hub-collar-"
  },
  {
   "feature": "hub-collar slit",
   "exact": "0.8",
   "mates": "closes on the tube / rod",
   "fit": "clamp",
   "files": "hub-collar-"
  },
  {
   "feature": "hub-collar pinch hole",
   "exact": "Ø2.5",
   "mates": "M3 tap drill",
   "fit": "designed",
   "files": "hub-collar-"
  }
 ],
 "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 is a flexure leaf fixed to the rod?",
   "a": "Between two split hub collars the size of the leaf's hub, pinched onto the rod with an M3 screw across a 0.8 mm slit."
  },
  {
   "q": "Which collar for the piston rod?",
   "a": "The b5 collar (Ø5 bore) on the 5 mm tube; b3 (Ø3 bore) on the displacer rod."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "hub-collar-60-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-collar-60-b5.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/hub-collar-60-b5.stl",
   "note": "split hub collar Ø13.2 × 6, Ø5 bore, 0.8 slit, M3 pinch (Ø2.5 tapped) across the slit at mid-thickness: clamps the leaf hubs on the 5 mm tube rod (two per stack)"
  },
  {
   "file": "hub-collar-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-collar-60-b3.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/hub-collar-60-b3.stl",
   "note": "split hub collar Ø13.2 × 6, Ø3 bore, 0.8 slit, M3 pinch (Ø2.5 tapped) across the slit at mid-thickness: clamps the leaf hubs on the Ø3 displacer rod (two per stack)"
  },
  {
   "file": "hub-collar-80-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-collar-80-b5.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/hub-collar-80-b5.stl",
   "note": "split hub collar Ø17.6 × 6, Ø5 bore, 0.8 slit, M3 pinch (Ø2.5 tapped) across the slit at mid-thickness: clamps the leaf hubs on the 5 mm tube rod (two per stack)"
  },
  {
   "file": "hub-collar-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-collar-80-b3.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/hub-collar-80-b3.stl",
   "note": "split hub collar Ø17.6 × 6, Ø3 bore, 0.8 slit, M3 pinch (Ø2.5 tapped) across the slit at mid-thickness: clamps the leaf hubs on the Ø3 displacer rod (two per stack)"
  },
  {
   "file": "hub-collar-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-collar-100-b5.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/hub-collar-100-b5.stl",
   "note": "split hub collar Ø22 × 6, Ø5 bore, 0.8 slit, M3 pinch (Ø2.5 tapped) across the slit at mid-thickness: clamps the leaf hubs on the 5 mm tube rod (two per stack)"
  },
  {
   "file": "hub-collar-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-collar-100-b3.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/hub-collar-100-b3.stl",
   "note": "split hub collar Ø22 × 6, Ø3 bore, 0.8 slit, M3 pinch (Ø2.5 tapped) across the slit at mid-thickness: clamps the leaf hubs on the Ø3 displacer rod (two per stack)"
  }
 ],
 "markdown": "https://xemstudio.com/objects/flexure-hub-collar/index.md"
}