{
 "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": "syringe-pistons",
 "name": "Syringe pistons: ring-less printed pistons with a con-rod fork for 10, 20 and 30 mL syringe barrels",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Drives & mechanisms",
 "year": null,
 "question": "How do I connect a syringe to a crank for a Stirling engine without the rubber plunger's friction?",
 "tags": [
  "syringe",
  "piston",
  "stirling",
  "alpha",
  "ross yoke",
  "gamma",
  "long earth society",
  "lapping"
 ],
 "aliases": [
  "syringe stirling engine piston",
  "replace syringe plunger stirling",
  "how to connect syringe plunger to crank",
  "10ml syringe piston stl",
  "low friction syringe piston"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": true,
 "free_files": 9,
 "url": "https://xemstudio.com/objects/syringe-pistons/",
 "sheet_txt": "https://xemstudio.com/objects/syringe-pistons/sheet.txt",
 "sheet": {
  "basis": "Barrel IDs from the plastic-syringes entry (10 mL 14.5, 20 mL 19.1, 30 mL 21.7 mm); same two-land, print-and-lap method as the tri-clamp power pistons",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "The rubber tip of a syringe plunger seals by squeezing the wall: far too much friction for a Stirling. Throw the plunger away and run a printed piston in the barrel instead, lapped to fit like the tri-clamp pistons (sinks slowly under its own weight, holds with the tip capped).",
   "Each piston has a 5 mm fork slot (exact: the con-rod thickness; see Mating features) open to the bottom and a Ø3 pin hole across it at 0.45 L: the Ross yoke kit's conrod-45 / conrod-60 (5 mm thick, Ø3 ends) or the crank kit's con-rods drop straight in on a 3 × 12 dowel. The fork keeps the con-rod inside the barrel's footprint, so the piston can enter the barrel past the pin.",
   "Fits: f008 / f015 are 0.08 / 0.15 mm under the barrel; lap is 0.08 over, to lap down. Plastic barrels vary by brand, so measure yours with calipers and pick the closest.",
   "Used by: the Ross yoke alpha (cylinder block for two 10 mL barrels), the alpha 90° V-block, the gamma power head (10 mL socket) and the can engine.",
   "LES: the syringe engines' pistons."
  ],
  "table": {
   "columns": [
    "syringe",
    "barrel_id_mm",
    "piston_od_mm",
    "length_mm",
    "offset_mm",
    "pin_z_mm"
   ],
   "rows": [
    [
     "10ml",
     14.5,
     14.58,
     19,
     "+0.08",
     8.6
    ],
    [
     "10ml",
     14.5,
     14.42,
     19,
     "-0.08",
     8.6
    ],
    [
     "10ml",
     14.5,
     14.35,
     19,
     "-0.15",
     8.6
    ],
    [
     "20ml",
     19.1,
     19.18,
     25,
     "+0.08",
     11.2
    ],
    [
     "20ml",
     19.1,
     19.02,
     25,
     "-0.08",
     11.2
    ],
    [
     "20ml",
     19.1,
     18.95,
     25,
     "-0.15",
     11.2
    ],
    [
     "30ml",
     21.7,
     21.78,
     28,
     "+0.08",
     12.6
    ],
    [
     "30ml",
     21.7,
     21.62,
     28,
     "-0.08",
     12.6
    ],
    [
     "30ml",
     21.7,
     21.55,
     28,
     "-0.15",
     12.6
    ]
   ]
  }
 },
 "sheet_text": "Syringe pistons: ring-less printed pistons with a con-rod fork for 10, 20 and 30 mL syringe barrels — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/syringe-pistons/  (CC BY 4.0)\nBasis: Barrel IDs from the plastic-syringes entry (10 mL 14.5, 20 mL 19.1, 30 mL 21.7 mm); same two-land, print-and-lap method as the tri-clamp power pistons\nCatalog version: 2026-10-20\n\nSizes: see table below\n- The rubber tip of a syringe plunger seals by squeezing the wall: far too much friction for a Stirling. Throw the plunger away and run a printed piston in the barrel instead, lapped to fit like the tri-clamp pistons (sinks slowly under its own weight, holds with the tip capped).\n- Each piston has a 5 mm fork slot (exact: the con-rod thickness; see Mating features) open to the bottom and a Ø3 pin hole across it at 0.45 L: the Ross yoke kit's conrod-45 / conrod-60 (5 mm thick, Ø3 ends) or the crank kit's con-rods drop straight in on a 3 × 12 dowel. The fork keeps the con-rod inside the barrel's footprint, so the piston can enter the barrel past the pin.\n- Fits: f008 / f015 are 0.08 / 0.15 mm under the barrel; lap is 0.08 over, to lap down. Plastic barrels vary by brand, so measure yours with calipers and pick the closest.\n- Used by: the Ross yoke alpha (cylinder block for two 10 mL barrels), the alpha 90° V-block, the gamma power head (10 mL socket) and the can engine.\n- LES: the syringe engines' pistons.\n\nsyringe  barrel_id_mm  piston_od_mm  length_mm  offset_mm  pin_z_mm\n10ml  14.5  14.58  19  +0.08  8.6\n10ml  14.5  14.42  19  -0.08  8.6\n10ml  14.5  14.35  19  -0.15  8.6\n20ml  19.1  19.18  25  +0.08  11.2\n20ml  19.1  19.02  25  -0.08  11.2\n20ml  19.1  18.95  25  -0.15  11.2\n30ml  21.7  21.78  28  +0.08  12.6\n30ml  21.7  21.62  28  -0.08  12.6\n30ml  21.7  21.55  28  -0.15  12.6\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\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, 9 parts): https://xemstudio.com/files/hardware/syringe-pistons/index.json\nAPI: https://xemstudio.com/api/geometry?object=syringe-pistons\n",
 "sources": [
  {
   "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": [
  "plastic-syringes",
  "ross-yoke-kit",
  "alpha-twin-crank-90",
  "crank-conrod-flywheel-kit",
  "dowel-pins-metric",
  "tri-clamp-displacers-and-heads",
  "can-engine-printed-kit"
 ],
 "fits": [
  {
   "role": "Goes in or on",
   "items": [
    {
     "slug": "plastic-syringes",
     "why": "runs in the barrel; plunger discarded"
    }
   ]
  },
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "alpha-v-twin-frame",
     "why": "two pistons in the alpha frame"
    },
    {
     "slug": "ross-yoke-kit",
     "why": "conrod-45 in the fork"
    },
    {
     "slug": "alpha-twin-crank-90",
     "why": "V-block alpha"
    },
    {
     "slug": "crank-conrod-flywheel-kit",
     "why": "con-rods"
    },
    {
     "slug": "can-engine-printed-kit",
     "why": "can engine power piston"
    }
   ]
  },
  {
   "role": "Alternatives",
   "items": [
    {
     "slug": "tri-clamp-power-pistons",
     "why": "full-bore tri-clamp pistons"
    },
    {
     "slug": "power-cylinder-piston-crosshead",
     "why": "Ø16–30 blanks in a printed liner"
    }
   ]
  },
  {
   "role": "Also needed",
   "items": [
    {
     "slug": "dowel-pins-metric",
     "why": "Ø3 × 12 piston pin"
    },
    {
     "slug": "printer-calibration-coupons",
     "why": "set the slicer first"
    }
   ]
  }
 ],
 "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 barrel",
   "exact": "barrel ID − 0.08 / − 0.15, lap +0.08",
   "mates": "syringe barrel (14.5 / 19.1 / 21.7)",
   "fit": "designed",
   "files": "all"
  },
  {
   "feature": "pin hole",
   "exact": "Ø3",
   "mates": "Ø3 pin",
   "fit": "press",
   "files": "all"
  },
  {
   "feature": "fork slot",
   "exact": "5",
   "mates": "5 mm thick con-rod (turns in it)",
   "fit": "run",
   "files": "all"
  },
  {
   "feature": "land relief",
   "exact": "OD − 0.5 between the lands",
   "mates": "barrel (no contact)",
   "fit": "designed",
   "files": "all"
  }
 ],
 "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": "Why replace the syringe plunger in a Stirling engine?",
   "a": "Its rubber seal's friction is larger than the force a small Stirling makes."
  },
  {
   "q": "How does the con-rod attach to a syringe piston?",
   "a": "The piston has a 5 mm fork slot and a Ø3 pin hole (both exact; see Mating features): drop a 5 mm thick con-rod (Ross conrod-45 or crank-kit rods) in and push a 3 × 12 dowel through."
  },
  {
   "q": "Which syringe piston do I print for a 10 mL syringe?",
   "a": "Measure the barrel bore; for the usual 14.5 mm print f008 (Ø14.42), lap to fit, and keep f015 as a spare if the barrel is tight."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "syringe-piston-10ml-lap",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/syringe-pistons/syringe-piston-10ml-lap.step",
   "stl": "https://xemstudio.com/files/hardware/syringe-pistons/syringe-piston-10ml-lap.stl",
   "note": "10ml syringe piston Ø14.58 × 19 (lapping stock, +0.08), two 5 mm lands, 5 mm fork slot (for a 5 mm thick con-rod), Ø3 pin hole at 8.6 mm"
  },
  {
   "file": "syringe-piston-10ml-f008",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/syringe-pistons/syringe-piston-10ml-f008.step",
   "stl": "https://xemstudio.com/files/hardware/syringe-pistons/syringe-piston-10ml-f008.stl",
   "note": "10ml syringe piston Ø14.42 × 19 (0.08 under the 14.5 barrel), two 5 mm lands, 5 mm fork slot (for a 5 mm thick con-rod), Ø3 pin hole at 8.6 mm"
  },
  {
   "file": "syringe-piston-10ml-f015",
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   "step": "https://xemstudio.com/files/hardware/syringe-pistons/syringe-piston-10ml-f015.step",
   "stl": "https://xemstudio.com/files/hardware/syringe-pistons/syringe-piston-10ml-f015.stl",
   "note": "10ml syringe piston Ø14.35 × 19 (0.15 under the 14.5 barrel), two 5 mm lands, 5 mm fork slot (for a 5 mm thick con-rod), Ø3 pin hole at 8.6 mm"
  },
  {
   "file": "syringe-piston-20ml-lap",
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    "step",
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   "stl": "https://xemstudio.com/files/hardware/syringe-pistons/syringe-piston-20ml-lap.stl",
   "note": "20ml syringe piston Ø19.18 × 25 (lapping stock, +0.08), two 5 mm lands, 5 mm fork slot (for a 5 mm thick con-rod), Ø3 pin hole at 11.2 mm"
  },
  {
   "file": "syringe-piston-20ml-f008",
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    "step",
    "stl"
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   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/syringe-pistons/syringe-piston-20ml-f008.step",
   "stl": "https://xemstudio.com/files/hardware/syringe-pistons/syringe-piston-20ml-f008.stl",
   "note": "20ml syringe piston Ø19.02 × 25 (0.08 under the 19.1 barrel), two 5 mm lands, 5 mm fork slot (for a 5 mm thick con-rod), Ø3 pin hole at 11.2 mm"
  },
  {
   "file": "syringe-piston-20ml-f015",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/syringe-pistons/syringe-piston-20ml-f015.step",
   "stl": "https://xemstudio.com/files/hardware/syringe-pistons/syringe-piston-20ml-f015.stl",
   "note": "20ml syringe piston Ø18.95 × 25 (0.15 under the 19.1 barrel), two 5 mm lands, 5 mm fork slot (for a 5 mm thick con-rod), Ø3 pin hole at 11.2 mm"
  },
  {
   "file": "syringe-piston-30ml-lap",
   "formats": [
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    "stl"
   ],
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   "license": "CC BY 4.0 (Xem Studio)",
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   "stl": "https://xemstudio.com/files/hardware/syringe-pistons/syringe-piston-30ml-lap.stl",
   "note": "30ml syringe piston Ø21.78 × 28 (lapping stock, +0.08), two 5 mm lands, 5 mm fork slot (for a 5 mm thick con-rod), Ø3 pin hole at 12.6 mm"
  },
  {
   "file": "syringe-piston-30ml-f008",
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    "stl"
   ],
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   "stl": "https://xemstudio.com/files/hardware/syringe-pistons/syringe-piston-30ml-f008.stl",
   "note": "30ml syringe piston Ø21.62 × 28 (0.08 under the 21.7 barrel), two 5 mm lands, 5 mm fork slot (for a 5 mm thick con-rod), Ø3 pin hole at 12.6 mm"
  },
  {
   "file": "syringe-piston-30ml-f015",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
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   "stl": "https://xemstudio.com/files/hardware/syringe-pistons/syringe-piston-30ml-f015.stl",
   "note": "30ml syringe piston Ø21.55 × 28 (0.15 under the 21.7 barrel), two 5 mm lands, 5 mm fork slot (for a 5 mm thick con-rod), Ø3 pin hole at 12.6 mm"
  }
 ],
 "markdown": "https://xemstudio.com/objects/syringe-pistons/index.md"
}