{
 "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-piston-plug",
 "name": "Tri-clamp piston plug: tube-rod socket for the -rod piston, 1.5, 2 and 3 in",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Free-piston",
 "year": null,
 "question": "How do I connect a tri-clamp piston to a flexure bearing?",
 "tags": [
  "free piston",
  "piston",
  "tri-clamp",
  "plug",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "how to connect a piston to a flexure bearing",
  "free piston plug",
  "piston rod adapter tri clamp",
  "tube rod socket piston"
 ],
 "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-piston-plug/",
 "sheet_txt": "https://xemstudio.com/objects/tri-clamp-piston-plug/sheet.txt",
 "sheet": {
  "basis": "Disc Ø = piston skirt bore (bore − 3.2: 31.6 / 44.3 / 69.7); legs pinned at the wrist-pin height 17.6 / 23.5 / 37.0; Ø5 × 15 tube socket; Ø3.4 rod passage",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "The plug that turns a -rod power piston into a free piston on a tube rod: it drops into the open skirt and is held by the two Ø3 wrist dowels through its legs.",
   "Disc Ø31.6 / Ø44.3 / Ø69.7 × 6 mm (the piston skirt bore, exact), two 4 × 9 legs up to the wrist-pin height with Ø3 pin holes at 17.6 / 23.5 / 37.0 mm.",
   "Below the disc: an Ø8 × 15 stub with a Ø5 × 15 socket for the 5 mm tube piston rod. A Ø3.4 passage runs through on centre so the Ø3 displacer rod clears it (the rod runs in the piston crown, not here).",
   "Overall height 38.6 / 44.5 / 58.0 mm."
  ],
  "table": {
   "columns": [
    "spool_in",
    "disc_od_mm",
    "pin_z_mm",
    "tube_socket_mm",
    "rod_passage_mm",
    "overall_h_mm"
   ],
   "rows": [
    [
     "1.5",
     31.6,
     17.6,
     "Ø5 × 15",
     3.4,
     38.6
    ],
    [
     "2",
     44.3,
     23.5,
     "Ø5 × 15",
     3.4,
     44.5
    ],
    [
     "3",
     69.7,
     37,
     "Ø5 × 15",
     3.4,
     58
    ]
   ]
  }
 },
 "sheet_text": "Tri-clamp piston plug: tube-rod socket for the -rod piston, 1.5, 2 and 3 in — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/tri-clamp-piston-plug/  (CC BY 4.0)\nBasis: Disc Ø = piston skirt bore (bore − 3.2: 31.6 / 44.3 / 69.7); legs pinned at the wrist-pin height 17.6 / 23.5 / 37.0; Ø5 × 15 tube socket; Ø3.4 rod passage\nCatalog version: 2026-10-20\n\nSizes: see table below\n- The plug that turns a -rod power piston into a free piston on a tube rod: it drops into the open skirt and is held by the two Ø3 wrist dowels through its legs.\n- Disc Ø31.6 / Ø44.3 / Ø69.7 × 6 mm (the piston skirt bore, exact), two 4 × 9 legs up to the wrist-pin height with Ø3 pin holes at 17.6 / 23.5 / 37.0 mm.\n- Below the disc: an Ø8 × 15 stub with a Ø5 × 15 socket for the 5 mm tube piston rod. A Ø3.4 passage runs through on centre so the Ø3 displacer rod clears it (the rod runs in the piston crown, not here).\n- Overall height 38.6 / 44.5 / 58.0 mm.\n\nspool_in  disc_od_mm  pin_z_mm  tube_socket_mm  rod_passage_mm  overall_h_mm\n1.5  31.6  17.6  Ø5 × 15  3.4  38.6\n2  44.3  23.5  Ø5 × 15  3.4  44.5\n3  69.7  37.0  Ø5 × 15  3.4  58.0\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-piston-plug/index.json\nAPI: https://xemstudio.com/api/geometry?object=tri-clamp-piston-plug\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-power-piston",
  "tri-clamp-flexure-head",
  "flexure-hub-collar",
  "dowel-pins-metric",
  "stirling-crankshafts"
 ],
 "fits": [
  {
   "role": "Goes in or on",
   "items": [
    {
     "slug": "tri-clamp-power-piston",
     "why": "disc in the -rod piston's skirt, on the Ø3 wrist dowels"
    }
   ]
  },
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "stirling-crankshafts",
     "why": "5 mm tube rod in the Ø5 × 15 socket"
    },
    {
     "slug": "flexure-hub-collar",
     "why": "b5 collars on the same tube"
    }
   ]
  },
  {
   "role": "Also needed",
   "items": [
    {
     "slug": "dowel-pins-metric",
     "why": "two Ø3 × 16 wrist dowels"
    }
   ]
  }
 ],
 "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": "piston plug disc in the skirt",
   "exact": "piston skirt bore (bore − 3.4)",
   "mates": "piston skirt",
   "fit": "slide",
   "files": "fp-piston-plug-"
  },
  {
   "feature": "plug wrist-pin holes",
   "exact": "Ø3",
   "mates": "Ø3 pins",
   "fit": "press",
   "files": "fp-piston-plug-"
  },
  {
   "feature": "plug tube socket",
   "exact": "Ø5 × 15",
   "mates": "5 mm tube",
   "fit": "press",
   "files": "fp-piston-plug-"
  },
  {
   "feature": "plug rod passage",
   "exact": "Ø3.4",
   "mates": "Ø3 rod (no contact)",
   "fit": "designed",
   "files": "fp-piston-plug-"
  }
 ],
 "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 does the piston connect to a flexure bearing?",
   "a": "Through the piston plug: it sits in the skirt on the wrist dowels and its Ø5 socket takes the 5 mm tube; the flexure hubs clamp on that tube."
  },
  {
   "q": "How does the displacer rod get past the piston plug?",
   "a": "Through a Ø3.4 passage on centre: the Ø3 rod clears the plug and runs on up inside the tube rod."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "fp-piston-plug-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-piston-plug-1.5in.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/fp-piston-plug-1.5in.stl",
   "note": "1.5 in piston plug: drops into the open skirt, two Ø3 × 16 wrist dowels through its legs at 17.6 mm retain it, Ø5 tube socket 15 deep, Ø3.4 clearance for the displacer rod (it runs in the piston's Ø3 crown bore, not here)"
  },
  {
   "file": "fp-piston-plug-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-piston-plug-2in.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/fp-piston-plug-2in.stl",
   "note": "2 in piston plug: drops into the open skirt, two Ø3 × 16 wrist dowels through its legs at 23.5 mm retain it, Ø5 tube socket 15 deep, Ø3.4 clearance for the displacer rod (it runs in the piston's Ø3 crown bore, not here)"
  },
  {
   "file": "fp-piston-plug-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-piston-plug-3in.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-free-piston-kit/fp-piston-plug-3in.stl",
   "note": "3 in piston plug: drops into the open skirt, two Ø3 × 16 wrist dowels through its legs at 37.0 mm retain it, Ø5 tube socket 15 deep, Ø3.4 clearance for the displacer rod (it runs in the piston's Ø3 crown bore, not here)"
  }
 ],
 "markdown": "https://xemstudio.com/objects/tri-clamp-piston-plug/index.md"
}