{
 "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": "power-piston",
 "name": "Power piston Ø16, 20, 25, 30 with Ø3 wrist-pin boss",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Drives & mechanisms",
 "year": null,
 "question": "What are the dimensions of a power piston for a Stirling engine power cylinder?",
 "tags": [
  "piston",
  "power piston",
  "wrist pin",
  "gamma",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "stirling power piston",
  "power piston 20 mm",
  "piston with wrist pin"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": true,
 "free_files": 8,
 "url": "https://xemstudio.com/objects/power-piston/",
 "sheet_txt": "https://xemstudio.com/objects/power-piston/sheet.txt",
 "sheet": {
  "basis": "Piston OD = liner bore (fit: run), length 0.9 × bore; Ø3 rod hole and Ø3 wrist-pin hole",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "The piston for the flanged liners, drawn at the liner bore exactly: Ø16 × 14, Ø20 × 18, Ø25 × 22, Ø30 × 27, with a 0.5 chamfer at the crown.",
   "Hollow with 2 mm walls; its closed end has a Ø3 hole (fit: slide) for a Ø3 piston rod.",
   "Inside the -blank piston, a wrist-pin bar across the bore carries a Ø3 hole (fit: press) at 0.4 × length + 4 from the closed end.",
   "Two kinds per bore: the -blank piston has a Ø3 rod hole in its crown and a solid wrist-pin bar (for a crosshead and piston rod); the -trunk piston has a closed 2 mm crown and two wrist-pin bosses 7 mm apart, so a 5 mm con-rod's small end (R7 eye) goes straight on its Ø3 wrist pin with 1 mm each side."
  ],
  "table": {
   "columns": [
    "file",
    "diameter",
    "length",
    "rod hole",
    "wrist-pin hole"
   ],
   "rows": [
    [
     "piston-16x14-blank",
     16,
     14,
     3,
     3
    ],
    [
     "piston-20x18-blank",
     20,
     18,
     3,
     3
    ],
    [
     "piston-25x22-blank",
     25,
     22,
     3,
     3
    ],
    [
     "piston-30x27-blank",
     30,
     27,
     3,
     3
    ]
   ]
  }
 },
 "sheet_text": "Power piston Ø16, 20, 25, 30 with Ø3 wrist-pin boss — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/power-piston/  (CC BY 4.0)\nBasis: Piston OD = liner bore (fit: run), length 0.9 × bore; Ø3 rod hole and Ø3 wrist-pin hole\nCatalog version: 2026-10-20\n\nSizes: see table below\n- The piston for the flanged liners, drawn at the liner bore exactly: Ø16 × 14, Ø20 × 18, Ø25 × 22, Ø30 × 27, with a 0.5 chamfer at the crown.\n- Hollow with 2 mm walls; its closed end has a Ø3 hole (fit: slide) for a Ø3 piston rod.\n- Inside the -blank piston, a wrist-pin bar across the bore carries a Ø3 hole (fit: press) at 0.4 × length + 4 from the closed end.\n- Two kinds per bore: the -blank piston has a Ø3 rod hole in its crown and a solid wrist-pin bar (for a crosshead and piston rod); the -trunk piston has a closed 2 mm crown and two wrist-pin bosses 7 mm apart, so a 5 mm con-rod's small end (R7 eye) goes straight on its Ø3 wrist pin with 1 mm each side.\n\nfile  diameter  length  rod hole  wrist-pin hole\npiston-16x14-blank  16  14  3  3\npiston-20x18-blank  20  18  3  3\npiston-25x22-blank  25  22  3  3\npiston-30x27-blank  30  27  3  3\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Wikipedia: Crosshead — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Crosshead\n- Wikipedia: Piston — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Piston\n- James R. Senft: Miniature Stirling engine piston fits (LTD book) — book — reference [verify license at link] — https://www.stirlingengine.com/\n- Long Earth Society: Engine builds — web, video — LES site — https://longearthsociety.com/engineering/\n\nFree files (CC BY 4.0, Xem Studio; STEP + STL, 8 parts): https://xemstudio.com/files/hardware/power-piston/index.json\nAPI: https://xemstudio.com/api/geometry?object=power-piston\n",
 "sources": [
  {
   "publisher": "Wikipedia",
   "title": "Crosshead",
   "url": "https://en.wikipedia.org/wiki/Crosshead",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text)",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Wikipedia",
   "title": "Piston",
   "url": "https://en.wikipedia.org/wiki/Piston",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text)",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "James R. Senft",
   "title": "Miniature Stirling engine piston fits (LTD book)",
   "url": "https://www.stirlingengine.com/",
   "formats": [
    "book"
   ],
   "license": "reference",
   "license_verified": false,
   "hosted": false
  },
  {
   "publisher": "Long Earth Society",
   "title": "Engine 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,
  "step_price_usd": null,
  "tolerance_mm": null
 },
 "related": [
  "power-cylinder-liner",
  "wrist-pin-3x16",
  "crosshead-8mm",
  "list-gamma-2in-tri-clamp"
 ],
 "fits": [
  {
   "role": "Goes in or on",
   "items": [
    {
     "slug": "power-cylinder-liner",
     "why": "in the liner of the same bore (run)"
    }
   ]
  },
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "wrist-pin-3x16",
     "why": "pin pressed in the boss"
    },
    {
     "slug": "crosshead-8mm",
     "why": "Ø3 piston rod to the crosshead"
    },
    {
     "slug": "crank-discs-5mm-bore",
     "why": "con-rod on the wrist pin (trunk style)"
    }
   ]
  },
  {
   "role": "Alternatives",
   "items": [
    {
     "slug": "syringe-pistons",
     "why": "syringe pistons"
    },
    {
     "slug": "free-piston-power-piston",
     "why": "Ø30 / Ø40 clearance-seal pistons"
    }
   ]
  }
 ],
 "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 liner",
   "exact": "Ø16 / Ø20 / Ø25 / Ø30 (= liner bore)",
   "mates": "liner bore (lapped clearance seal)",
   "fit": "run",
   "files": "piston-"
  },
  {
   "feature": "piston rod hole",
   "exact": "Ø3",
   "mates": "Ø3 piston rod",
   "fit": "slide",
   "files": "piston-"
  },
  {
   "feature": "piston wrist-pin hole",
   "exact": "Ø3",
   "mates": "wrist-pin-3x16",
   "fit": "press",
   "files": "piston-"
  },
  {
   "feature": "trunk-piston boss gap",
   "exact": "7",
   "mates": "5 mm con-rod small end, R7 eye (no contact)",
   "fit": "designed",
   "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 size piston goes in the 20 mm liner?",
   "a": "Ø20 × 18, drawn at the bore; the fit is run (see Mating features)."
  },
  {
   "q": "Does the piston need a crosshead?",
   "a": "With a crosshead the piston only moves axially; trunk style, the con-rod goes straight on the wrist pin, fine for rods at least 4 × the stroke."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "piston-16x14-blank",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/piston-16x14-blank.step",
   "stl": "https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/piston-16x14-blank.stl",
   "note": "piston Ø16 (= the liner bore; clearance-seal running fit) × 14: Ø3 rod hole and a Ø3 wrist-pin boss"
  },
  {
   "file": "piston-16x14-trunk",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/piston-16x14-trunk.step",
   "stl": "https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/piston-16x14-trunk.stl",
   "note": "trunk piston Ø16 (= the liner bore) × 14: closed 2 mm crown, open skirt, two wrist-pin bosses 7 apart for a 5 mm con-rod's small end, Ø3 wrist pin across the bore 9.6 above the crown face"
  },
  {
   "file": "piston-20x18-blank",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/piston-20x18-blank.step",
   "stl": "https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/piston-20x18-blank.stl",
   "note": "piston Ø20 (= the liner bore; clearance-seal running fit) × 18: Ø3 rod hole and a Ø3 wrist-pin boss"
  },
  {
   "file": "piston-20x18-trunk",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/piston-20x18-trunk.step",
   "stl": "https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/piston-20x18-trunk.stl",
   "note": "trunk piston Ø20 (= the liner bore) × 18: closed 2 mm crown, open skirt, two wrist-pin bosses 7 apart for a 5 mm con-rod's small end, Ø3 wrist pin across the bore 11.2 above the crown face"
  },
  {
   "file": "piston-25x22-blank",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/piston-25x22-blank.step",
   "stl": "https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/piston-25x22-blank.stl",
   "note": "piston Ø25 (= the liner bore; clearance-seal running fit) × 22: Ø3 rod hole and a Ø3 wrist-pin boss"
  },
  {
   "file": "piston-25x22-trunk",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/piston-25x22-trunk.step",
   "stl": "https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/piston-25x22-trunk.stl",
   "note": "trunk piston Ø25 (= the liner bore) × 22: closed 2 mm crown, open skirt, two wrist-pin bosses 7 apart for a 5 mm con-rod's small end, Ø3 wrist pin across the bore 12.8 above the crown face"
  },
  {
   "file": "piston-30x27-blank",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/piston-30x27-blank.step",
   "stl": "https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/piston-30x27-blank.stl",
   "note": "piston Ø30 (= the liner bore; clearance-seal running fit) × 27: Ø3 rod hole and a Ø3 wrist-pin boss"
  },
  {
   "file": "piston-30x27-trunk",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/piston-30x27-trunk.step",
   "stl": "https://xemstudio.com/files/hardware/power-cylinder-piston-crosshead/piston-30x27-trunk.stl",
   "note": "trunk piston Ø30 (= the liner bore) × 27: closed 2 mm crown, open skirt, two wrist-pin bosses 7 apart for a 5 mm con-rod's small end, Ø3 wrist pin across the bore 14.8 above the crown face"
  }
 ],
 "markdown": "https://xemstudio.com/objects/power-piston/index.md"
}