{
 "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-displacer-head",
 "name": "Tri-clamp displacer head: ISO 2852 cap with Ø3 rod bore and 4 mm barb, 1.5, 2 and 3 in",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Tri-clamp engine parts",
 "year": null,
 "question": "What end cap guides the displacer rod out of a tri-clamp Stirling cylinder?",
 "tags": [
  "tri-clamp",
  "end cap",
  "displacer rod",
  "stirling",
  "gamma",
  "rod guide",
  "long earth society"
 ],
 "aliases": [
  "tri clamp end cap with rod guide",
  "stirling displacer head",
  "tri clamp cap 3mm rod",
  "gamma stirling cold head",
  "tri clamp cap with hose barb"
 ],
 "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-displacer-head/",
 "sheet_txt": "https://xemstudio.com/objects/tri-clamp-displacer-head/sheet.txt",
 "sheet": {
  "basis": "ISO 2852 cap face (Ø50.5 / 64.0 / 91.0 flange, 6 mm cap) with a Ø3 run bore on centre and a 4 mm hose barb",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "An ISO 2852 end cap with the displacer-rod guide and a transfer port on its back, so a stock clamp and Type B gasket seal it to any ferrule of its size.",
   "On centre: a Ø3 bore straight through cap and boss for the Ø3 displacer rod (run fit). The bore is the rod guide and the clearance seal; nothing is pressed into it.",
   "Off centre: an integral 4 mm hose barb (Ø6.4 base, Ø3.2 bore) for the transfer tube to the power cylinder, at 13.75 / 20.25 / 33.75 mm from the axis on the 1.5 / 2 / 3 in head.",
   "Flange Ø50.5 (1.5 in, also fits 1 in ferrules), Ø64.0 (2 in), Ø91.0 (3 in)."
  ],
  "table": {
   "columns": [
    "size_in",
    "flange_od_mm",
    "rod_bore_mm",
    "barb",
    "barb_offset_mm"
   ],
   "rows": [
    [
     "1.5",
     50.5,
     3,
     "4 mm (Ø6.4, Ø3.2 bore)",
     13.75
    ],
    [
     "2",
     64,
     3,
     "4 mm (Ø6.4, Ø3.2 bore)",
     20.25
    ],
    [
     "3",
     91,
     3,
     "4 mm (Ø6.4, Ø3.2 bore)",
     33.75
    ]
   ]
  }
 },
 "sheet_text": "Tri-clamp displacer head: ISO 2852 cap with Ø3 rod bore and 4 mm barb, 1.5, 2 and 3 in — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/tri-clamp-displacer-head/  (CC BY 4.0)\nBasis: ISO 2852 cap face (Ø50.5 / 64.0 / 91.0 flange, 6 mm cap) with a Ø3 run bore on centre and a 4 mm hose barb\nCatalog version: 2026-10-20\n\nSizes: see table below\n- An ISO 2852 end cap with the displacer-rod guide and a transfer port on its back, so a stock clamp and Type B gasket seal it to any ferrule of its size.\n- On centre: a Ø3 bore straight through cap and boss for the Ø3 displacer rod (run fit). The bore is the rod guide and the clearance seal; nothing is pressed into it.\n- Off centre: an integral 4 mm hose barb (Ø6.4 base, Ø3.2 bore) for the transfer tube to the power cylinder, at 13.75 / 20.25 / 33.75 mm from the axis on the 1.5 / 2 / 3 in head.\n- Flange Ø50.5 (1.5 in, also fits 1 in ferrules), Ø64.0 (2 in), Ø91.0 (3 in).\n\nsize_in  flange_od_mm  rod_bore_mm  barb  barb_offset_mm\n1.5  50.5  3  4 mm (Ø6.4, Ø3.2 bore)  13.75\n2  64.0  3  4 mm (Ø6.4, Ø3.2 bore)  20.25\n3  91.0  3  4 mm (Ø6.4, Ø3.2 bore)  33.75\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 Low Temperature Differential Stirling Engines (displacer and gap design) — book — Moriya Press [verify license at link] — https://www.stirlingengine.com/\n- Wikipedia: Stirling engine — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Stirling_engine\n\nFree files (CC BY 4.0, Xem Studio; STEP + STL, 3 parts): https://xemstudio.com/files/hardware/tri-clamp-displacer-head/index.json\nAPI: https://xemstudio.com/api/geometry?object=tri-clamp-displacer-head\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 Low Temperature Differential Stirling Engines (displacer and gap design)",
   "url": "https://www.stirlingengine.com/",
   "formats": [
    "book"
   ],
   "license": "Moriya Press",
   "license_verified": false,
   "hosted": false
  },
  {
   "publisher": "Wikipedia",
   "title": "Stirling engine",
   "url": "https://en.wikipedia.org/wiki/Stirling_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-displacer",
  "tri-clamp-syringe-head",
  "tri-clamp-crank-head",
  "tri-clamp-clamps",
  "silicone-tube",
  "tri-clamp-end-cap"
 ],
 "fits": [
  {
   "role": "Goes in or on",
   "items": [
    {
     "slug": "tri-clamp-spool",
     "why": "ISO 2852 face on the spool ferrule"
    }
   ]
  },
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "tri-clamp-displacer",
     "why": "Ø3 rod from the displacer cap through the Ø3 bore"
    },
    {
     "slug": "silicone-tube",
     "why": "4 mm ID tube on the transfer barb"
    },
    {
     "slug": "tri-clamp-syringe-head",
     "why": "transfer tube to the power cylinder"
    }
   ]
  },
  {
   "role": "Alternatives",
   "items": [
    {
     "slug": "tri-clamp-crank-head",
     "why": "rod bore plus crank towers in one head"
    }
   ]
  },
  {
   "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": "head faces",
   "exact": "ISO 2852",
   "mates": "ferrule face + Type B gasket",
   "fit": "clamp",
   "files": "head-"
  },
  {
   "feature": "transfer-port barb",
   "exact": "Ø6.4 barb, Ø3.2 bore",
   "mates": "4 mm ID tube",
   "fit": "designed",
   "files": "head-displacer-"
  },
  {
   "feature": "rod-guide bore",
   "exact": "Ø3 × 16.4 (through cap and Ø10 boss)",
   "mates": "Ø3 displacer rod",
   "fit": "run",
   "files": "head-displacer-"
  }
 ],
 "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 displacer rod get out of a tri-clamp cylinder?",
   "a": "Through the Ø3 bore on the centre of this head: the Ø3 rod runs in it, and the bore length is the clearance seal."
  },
  {
   "q": "What is the barb on the displacer head for?",
   "a": "The transfer port: a 4 mm barb (Ø6.4 base, Ø3.2 bore) for the tube to the power cylinder."
  },
  {
   "q": "Does it need a special clamp?",
   "a": "No: the face is ISO 2852, so a stock clamp and Type B gasket for the flange size seal it."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "head-displacer-1.5in",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/head-displacer-1.5in.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/head-displacer-1.5in.stl",
   "note": "1.5 in ISO 2852 cap: Ø3 rod-guide bore straight through the cap and its Ø10 × 12 boss for the Ø3 displacer rod (running fit, see Mating features); 4 mm transfer-port barb"
  },
  {
   "file": "head-displacer-2in",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/head-displacer-2in.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/head-displacer-2in.stl",
   "note": "2 in ISO 2852 cap: Ø3 rod-guide bore straight through the cap and its Ø10 × 12 boss for the Ø3 displacer rod (running fit, see Mating features); 4 mm transfer-port barb"
  },
  {
   "file": "head-displacer-3in",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/head-displacer-3in.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-displacers-and-heads/head-displacer-3in.stl",
   "note": "3 in ISO 2852 cap: Ø3 rod-guide bore straight through the cap and its Ø10 × 12 boss for the Ø3 displacer rod (running fit, see Mating features); 4 mm transfer-port barb"
  }
 ],
 "markdown": "https://xemstudio.com/objects/tri-clamp-displacer-head/index.md"
}