{
 "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": "silicone-tube-and-fittings",
 "name": "Silicone and PU tube, hose barbs and push-fit fittings (the transfer port)",
 "kind": "hardware",
 "category": "Hardware",
 "group": "Pipe & fittings",
 "year": null,
 "question": "What size silicone tube and barb for a Stirling engine transfer port?",
 "tags": [
  "tube",
  "hose",
  "barb",
  "push fit",
  "silicone",
  "pneumatic",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "silicone tube sizes",
  "hose barb size for 4mm tube",
  "push fit fitting 6mm",
  "pu tube 6x4",
  "pneumatic tube sizes",
  "transfer port stirling"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": true,
 "free_files": 22,
 "url": "https://xemstudio.com/objects/silicone-tube-and-fittings/",
 "sheet_txt": "https://xemstudio.com/objects/silicone-tube-and-fittings/sheet.txt",
 "sheet": {
  "basis": "Common silicone tube sizes (ID × OD, 1–2 mm wall), ISO 6432-style PU pneumatic tube (4/6/8/10/12 mm OD), barb geometry (OD = tube ID + 1.2, 3 barbs), push-fit envelopes",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "Silicone tube ID × OD: 1×3, 2×4, 3×5, 4×6, 5×8, 6×9, 8×12, 10×14 mm; 60 Shore A, −60 to 200 °C, stretches over a barb 1.5 mm larger than its ID. PU pneumatic tube (push-fit): 4×2.5, 6×4, 8×5.5, 10×6.5, 12×8 OD×ID; stiff, rated 10 bar, 80 °C max.",
   "Transfer port on a can/test-tube Stirling: 4 mm ID silicone, as short as possible (every mL of tube is dead volume that costs compression ratio); the can-cap port is Ø4.2 for a 4 mm barb. Larger engines: 6–8 mm ID.",
   "Barbs: OD = tube ID + 1.2 mm, three 2.5 mm barbs, a hex base; printed barbs seal silicone tube fine (sand the layer lines). Push-fit fittings take the PU tube OD exactly: 6 mm tube into a 6 mm fitting; thread stubs G1/8 (9.73 OD) or G1/4 (13.16).",
   "LES: 4 × 6 silicone between the hot and cold spools on the demonstrators; 6 mm PU + push-fits on the pressurised engines."
  ],
  "table": {
   "columns": [
    "tube",
    "id_mm",
    "od_mm",
    "wall_mm",
    "barb_od_mm"
   ],
   "rows": [
    [
     "silicone",
     1,
     3,
     1,
     2.2
    ],
    [
     "silicone",
     2,
     4,
     1,
     3.2
    ],
    [
     "silicone",
     3,
     5,
     1,
     4.2
    ],
    [
     "silicone",
     4,
     6,
     1,
     5.2
    ],
    [
     "silicone",
     5,
     8,
     1.5,
     6.2
    ],
    [
     "silicone",
     6,
     9,
     1.5,
     7.2
    ],
    [
     "silicone",
     8,
     12,
     2,
     9.2
    ],
    [
     "silicone",
     10,
     14,
     2,
     11.2
    ],
    [
     "PU push-fit",
     2.5,
     4,
     0.75,
     "push-fit"
    ],
    [
     "PU push-fit",
     4,
     6,
     1,
     "push-fit"
    ],
    [
     "PU push-fit",
     5.5,
     8,
     1.25,
     "push-fit"
    ],
    [
     "PU push-fit",
     6.5,
     10,
     1.75,
     "push-fit"
    ],
    [
     "PU push-fit",
     8,
     12,
     2,
     "push-fit"
    ]
   ]
  }
 },
 "sheet_text": "Silicone and PU tube, hose barbs and push-fit fittings (the transfer port) — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/silicone-tube-and-fittings/  (CC BY 4.0)\nBasis: Common silicone tube sizes (ID × OD, 1–2 mm wall), ISO 6432-style PU pneumatic tube (4/6/8/10/12 mm OD), barb geometry (OD = tube ID + 1.2, 3 barbs), push-fit envelopes\nCatalog version: 2026-10-20\n\nSizes: see table below\n- Silicone tube ID × OD: 1×3, 2×4, 3×5, 4×6, 5×8, 6×9, 8×12, 10×14 mm; 60 Shore A, −60 to 200 °C, stretches over a barb 1.5 mm larger than its ID. PU pneumatic tube (push-fit): 4×2.5, 6×4, 8×5.5, 10×6.5, 12×8 OD×ID; stiff, rated 10 bar, 80 °C max.\n- Transfer port on a can/test-tube Stirling: 4 mm ID silicone, as short as possible (every mL of tube is dead volume that costs compression ratio); the can-cap port is Ø4.2 for a 4 mm barb. Larger engines: 6–8 mm ID.\n- Barbs: OD = tube ID + 1.2 mm, three 2.5 mm barbs, a hex base; printed barbs seal silicone tube fine (sand the layer lines). Push-fit fittings take the PU tube OD exactly: 6 mm tube into a 6 mm fitting; thread stubs G1/8 (9.73 OD) or G1/4 (13.16).\n- LES: 4 × 6 silicone between the hot and cold spools on the demonstrators; 6 mm PU + push-fits on the pressurised engines.\n\ntube  id_mm  od_mm  wall_mm  barb_od_mm\nsilicone  1  3  1.0  2.2\nsilicone  2  4  1.0  3.2\nsilicone  3  5  1.0  4.2\nsilicone  4  6  1.0  5.2\nsilicone  5  8  1.5  6.2\nsilicone  6  9  1.5  7.2\nsilicone  8  12  2.0  9.2\nsilicone  10  14  2.0  11.2\nPU push-fit  2.5  4  0.75  push-fit\nPU push-fit  4  6  1.0  push-fit\nPU push-fit  5.5  8  1.25  push-fit\nPU push-fit  6.5  10  1.75  push-fit\nPU push-fit  8  12  2.0  push-fit\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Wikipedia: Hose barb — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Hose_barb\n- Wikipedia: Push-fit fitting — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Push-to-connect_fitting\n- McMaster-Carr: Tubing (free STEP per part, for your own design use; no redistribution) — STEP, PDF — McMaster-Carr site terms [verify license at link] — https://www.mcmaster.com/products/tubing/\n- Long Earth Society: Engine and rig builds — web, video — LES site — https://longearthsociety.com/engineering/\n\nFree files (CC BY 4.0, Xem Studio; STEP + STL, 22 parts): https://xemstudio.com/files/hardware/silicone-tube-and-fittings/index.json\nAPI: https://xemstudio.com/api/geometry?object=silicone-tube-and-fittings\n",
 "sources": [
  {
   "publisher": "Wikipedia",
   "title": "Hose barb",
   "url": "https://en.wikipedia.org/wiki/Hose_barb",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text)",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Wikipedia",
   "title": "Push-fit fitting",
   "url": "https://en.wikipedia.org/wiki/Push-to-connect_fitting",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text)",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "McMaster-Carr",
   "title": "Tubing (free STEP per part, for your own design use; no redistribution)",
   "url": "https://www.mcmaster.com/products/tubing/",
   "formats": [
    "STEP",
    "PDF"
   ],
   "license": "McMaster-Carr site terms",
   "license_verified": false,
   "hosted": false
  },
  {
   "publisher": "Long Earth Society",
   "title": "Engine and rig builds",
   "url": "https://longearthsociety.com/engineering/",
   "formats": [
    "web",
    "video"
   ],
   "license": "LES site",
   "license_verified": true,
   "hosted": false
  }
 ],
 "xem": {
  "status": "free-files",
  "sheet_free": true,
  "mesh_price_usd": null,
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  "tolerance_mm": null
 },
 "related": [
  "npt-bsp-thread-envelopes",
  "can-engine-printed-kit",
  "plastic-syringes",
  "o-rings-metric",
  "copper-pipe-type-l-m"
 ],
 "faq": [
  {
   "q": "What silicone tube for a Stirling transfer port?",
   "a": "4 mm ID × 6 mm OD, kept under 30 mm long; the can-cap port is Ø4.2 for a 4 mm barb."
  },
  {
   "q": "What barb size for 6 mm ID silicone tube?",
   "a": "7.2 mm barb OD (ID + 1.2), three barbs 2.5 mm long; silicone stretches on and seals without a clamp at low pressure."
  },
  {
   "q": "What is the ID of 6 mm PU pneumatic tube?",
   "a": "4 mm (6 × 4); 8 mm tube is 5.5 ID, 4 mm tube is 2.5 ID."
  }
 ],
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  },
  {
   "file": "barb-2mm",
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   "stl": "https://xemstudio.com/files/hardware/silicone-tube-and-fittings/barb-2mm.stl",
   "note": "hose barb for 2 mm ID tube, 3 barbs, hex base; print and tap or glue"
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   "note": "hose barb for 3 mm ID tube, 3 barbs, hex base; print and tap or glue"
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   "stl": "https://xemstudio.com/files/hardware/silicone-tube-and-fittings/barb-4mm.stl",
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   "note": "push-fit fitting envelope: 6 mm tube, G1/8 thread stub"
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   "stl": "https://xemstudio.com/files/hardware/silicone-tube-and-fittings/pushfit-6mm-g1-4.stl",
   "note": "push-fit fitting envelope: 6 mm tube, G1/4 thread stub"
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 "markdown": "https://xemstudio.com/objects/silicone-tube-and-fittings/index.md"
}