{
 "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-power-piston",
 "name": "Tri-clamp power piston: ring-less full-bore pistons Ø34.8, Ø47.5 and Ø72.9",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Tri-clamp engine parts",
 "year": null,
 "question": "What size power piston fits a 2 inch tri-clamp spool?",
 "tags": [
  "piston",
  "power piston",
  "tri-clamp",
  "stirling",
  "ring-less",
  "beta",
  "alpha",
  "long earth society"
 ],
 "aliases": [
  "piston for 2 inch tri clamp spool",
  "stirling power piston no o-ring",
  "ring-less piston clearance",
  "tri clamp piston stl",
  "47.5 mm piston"
 ],
 "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/tri-clamp-power-piston/",
 "sheet_txt": "https://xemstudio.com/objects/tri-clamp-power-piston/sheet.txt",
 "sheet": {
  "basis": "16 ga ASME BPE bores 34.8 / 47.5 / 72.9 mm; piston drawn at the bore diameter; length 1.2 × bore",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "A ring-less full-bore piston: no ring and no O-ring, the seal is the fit in the spool bore. The piston is drawn at exactly the bore, Ø34.8 / 47.5 / 72.9; its running fit to the bore (0.02–0.05 mm on diameter for a clearance seal) is listed under Mating features.",
   "Length 42 / 56 / 88 mm (1.2 × bore). Two 8 mm full-diameter lands at the ends carry the fit; between them the body is relieved 0.4 mm on radius. Crown 2.5 mm, skirt wall 1.6 mm, open skirt.",
   "Wrist-pin bosses cross the skirt at 0.42 L (17.6 / 23.5 / 37.0 mm from the open end) with a Ø3 pin bore; the gap between the bosses is 16 mm (1.5 in) or 18 mm (2 and 3 in) for the con-rod small end.",
   "The -rod pistons add a Ø11 × 6 boss under the crown with a Ø3 bore through crown and boss (8.5 long): the Ø3 displacer rod runs through it (beta, rhombic, free-piston layouts).",
   "The 2 in piston is about 16.8 cm³ of material."
  ],
  "table": {
   "columns": [
    "spool_in",
    "bore_mm",
    "piston_od_mm",
    "length_mm",
    "wrist_pin_z_mm",
    "files"
   ],
   "rows": [
    [
     "1.5",
     34.8,
     34.8,
     42,
     17.6,
     "piston-1.5in, piston-1.5in-rod"
    ],
    [
     "2",
     47.5,
     47.5,
     56,
     23.5,
     "piston-2in, piston-2in-rod"
    ],
    [
     "3",
     72.9,
     72.9,
     88,
     37,
     "piston-3in, piston-3in-rod"
    ]
   ]
  }
 },
 "sheet_text": "Tri-clamp power piston: ring-less full-bore pistons Ø34.8, Ø47.5 and Ø72.9 — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/tri-clamp-power-piston/  (CC BY 4.0)\nBasis: 16 ga ASME BPE bores 34.8 / 47.5 / 72.9 mm; piston drawn at the bore diameter; length 1.2 × bore\nCatalog version: 2026-10-20\n\nSizes: see table below\n- A ring-less full-bore piston: no ring and no O-ring, the seal is the fit in the spool bore. The piston is drawn at exactly the bore, Ø34.8 / 47.5 / 72.9; its running fit to the bore (0.02–0.05 mm on diameter for a clearance seal) is listed under Mating features.\n- Length 42 / 56 / 88 mm (1.2 × bore). Two 8 mm full-diameter lands at the ends carry the fit; between them the body is relieved 0.4 mm on radius. Crown 2.5 mm, skirt wall 1.6 mm, open skirt.\n- Wrist-pin bosses cross the skirt at 0.42 L (17.6 / 23.5 / 37.0 mm from the open end) with a Ø3 pin bore; the gap between the bosses is 16 mm (1.5 in) or 18 mm (2 and 3 in) for the con-rod small end.\n- The -rod pistons add a Ø11 × 6 boss under the crown with a Ø3 bore through crown and boss (8.5 long): the Ø3 displacer rod runs through it (beta, rhombic, free-piston layouts).\n- The 2 in piston is about 16.8 cm³ of material.\n\nspool_in  bore_mm  piston_od_mm  length_mm  wrist_pin_z_mm  files\n1.5  34.8  34.8  42  17.6  piston-1.5in, piston-1.5in-rod\n2  47.5  47.5  56  23.5  piston-2in, piston-2in-rod\n3  72.9  72.9  88  37.0  piston-3in, piston-3in-rod\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Long Earth Society: Tri-clamp Stirling engine builds — web, video — LES site — https://longearthsociety.com/engineering/\n- James R. Senft: An Introduction to Stirling Engines (piston fit and leakage) — book — Moriya Press [verify license at link] — https://www.stirlingengine.com/\n- ASME: BPE tube dimensions (16 ga sanitary tube) — standard — ASME [verify license at link] — https://www.asme.org/codes-standards/find-codes-standards/bpe-bioprocessing-equipment\n\nFree files (CC BY 4.0, Xem Studio; STEP + STL, 6 parts): https://xemstudio.com/files/hardware/tri-clamp-power-piston/index.json\nAPI: https://xemstudio.com/api/geometry?object=tri-clamp-power-piston\n",
 "sources": [
  {
   "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": "James R. Senft",
   "title": "An Introduction to Stirling Engines (piston fit and leakage)",
   "url": "https://www.stirlingengine.com/",
   "formats": [
    "book"
   ],
   "license": "Moriya Press",
   "license_verified": false,
   "hosted": false
  },
  {
   "publisher": "ASME",
   "title": "BPE tube dimensions (16 ga sanitary tube)",
   "url": "https://www.asme.org/codes-standards/find-codes-standards/bpe-bioprocessing-equipment",
   "formats": [
    "standard"
   ],
   "license": "ASME",
   "license_verified": false,
   "hosted": false
  }
 ],
 "xem": {
  "status": "free-files",
  "sheet_free": true,
  "mesh_price_usd": null,
  "step_price_usd": null,
  "tolerance_mm": null
 },
 "related": [
  "tri-clamp-con-rod",
  "tri-clamp-crank-frame",
  "tri-clamp-piston-plug",
  "tri-clamp-spool",
  "dowel-pins-metric"
 ],
 "fits": [
  {
   "role": "Parts that fit it",
   "items": [
    {
     "slug": "stirling-crankshafts",
     "why": "Ø8 shaft in the crank frame's 608s"
    }
   ]
  },
  {
   "role": "Goes in or on",
   "items": [
    {
     "slug": "tri-clamp-spool",
     "why": "piston OD in the 34.8 / 47.5 / 72.9 bore"
    },
    {
     "slug": "tri-clamp-cups",
     "why": "same bore, closed end"
    }
   ]
  },
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "tri-clamp-con-rod",
     "why": "623 in the rod small end on the Ø3 wrist pin"
    },
    {
     "slug": "tri-clamp-piston-plug",
     "why": "plug in the -rod piston's skirt on the wrist pins"
    }
   ]
  },
  {
   "role": "Alternatives",
   "items": [
    {
     "slug": "power-cylinder-liner",
     "why": "small-bore pistons in their own liner"
    }
   ]
  },
  {
   "role": "Also needed",
   "items": [
    {
     "slug": "dowel-pins-metric",
     "why": "Ø3 wrist pin"
    }
   ]
  }
 ],
 "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 OD in the spool bore",
   "exact": "Ø34.8 / 47.5 / 72.9 (= bore)",
   "mates": "tri-clamp-spool bore (ring-less clearance seal)",
   "fit": "run",
   "files": "piston-"
  },
  {
   "feature": "wrist-pin bore",
   "exact": "Ø3",
   "mates": "Ø3 pin (stirling-shafts-and-rods pin-3x…)",
   "fit": "press",
   "files": "piston-"
  },
  {
   "feature": "wrist-pin boss gap",
   "exact": "16 / 18",
   "mates": "con-rod small end",
   "fit": "designed",
   "files": "piston-"
  },
  {
   "feature": "crown rod bore (-rod pistons)",
   "exact": "Ø3 × 8.5 (crown + boss)",
   "mates": "Ø3 displacer rod (slides through it)",
   "fit": "run",
   "files": "piston-"
  }
 ],
 "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 clearance does a ring-less Stirling piston need?",
   "a": "A running fit of 0.02–0.05 mm on diameter. The piston is drawn at the bore diameter; that fit is its mating feature, set by whoever makes it."
  },
  {
   "q": "Which piston fits a 2 inch spool?",
   "a": "The 2 in piston: Ø47.5 (the bore), 56 mm long, with the Ø3 wrist pin 23.5 mm from the open end."
  },
  {
   "q": "Why two lands with a relief between?",
   "a": "Only the two 8 mm end lands touch the bore; the 0.4 mm relief between them halves the rubbing area while the full length keeps the piston square."
  },
  {
   "q": "What is the -rod piston?",
   "a": "The same piston with a Ø3 bore through the crown and an Ø11 crown boss, so the Ø3 displacer rod runs through the piston."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "piston-1.5in",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-1.5in.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-1.5in.stl",
   "note": "1.5 in full-bore piston Ø34.8 × 42 (the spool bore, exact), two 8 mm lands with 0.4 relief between, Ø3 wrist pin at 17.6 mm, open skirt"
  },
  {
   "file": "piston-1.5in-rod",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-1.5in-rod.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-1.5in-rod.stl",
   "note": "1.5 in piston Ø34.8 as above with a Ø3 bore through the crown and a Ø11 × 6 boss under it: the Ø3 displacer rod runs through it (beta, rhombic, free-piston)"
  },
  {
   "file": "piston-2in",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-2in.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-2in.stl",
   "note": "2 in full-bore piston Ø47.5 × 56 (the spool bore, exact), two 8 mm lands with 0.4 relief between, Ø3 wrist pin at 23.5 mm, open skirt"
  },
  {
   "file": "piston-2in-rod",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-2in-rod.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-2in-rod.stl",
   "note": "2 in piston Ø47.5 as above with a Ø3 bore through the crown and a Ø11 × 6 boss under it: the Ø3 displacer rod runs through it (beta, rhombic, free-piston)"
  },
  {
   "file": "piston-3in",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-3in.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-3in.stl",
   "note": "3 in full-bore piston Ø72.9 × 88 (the spool bore, exact), two 8 mm lands with 0.4 relief between, Ø3 wrist pin at 37.0 mm, open skirt"
  },
  {
   "file": "piston-3in-rod",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-3in-rod.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-power-pistons/piston-3in-rod.stl",
   "note": "3 in piston Ø72.9 as above with a Ø3 bore through the crown and a Ø11 × 6 boss under it: the Ø3 displacer rod runs through it (beta, rhombic, free-piston)"
  }
 ],
 "markdown": "https://xemstudio.com/objects/tri-clamp-power-piston/index.md"
}