{
 "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": "four-bar-links",
 "name": "Four-bar links: flat links with 20 to 100 mm hole centres",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Drives & mechanisms",
 "year": null,
 "question": "Where can I get 3D printable linkage bars for a four-bar mechanism?",
 "tags": [
  "four bar linkage",
  "link",
  "linkage",
  "rocker",
  "mechanism",
  "motion",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "four bar linkage parts",
  "linkage bar stl",
  "3d printed linkage",
  "meccano style link"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": true,
 "free_files": 7,
 "url": "https://xemstudio.com/objects/four-bar-links/",
 "sheet_txt": "https://xemstudio.com/objects/four-bar-links/sheet.txt",
 "sheet": {
  "basis": "Flat links 10 wide × 5 thick, Ø3 holes at exact centres from 20 to 100 mm",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "Seven lengths: 20, 30, 40, 50, 60, 80 and 100 mm between hole centres.",
   "Ø3 holes at both ends for Ø3 pins, so links pin to each other, to the bell cranks and to the Scotch yoke rod.",
   "Builds crank-rockers, parallel motions, rocking beams and the Ross yoke linkage."
  ],
  "table": {
   "columns": [
    "centres",
    "width × thickness",
    "holes"
   ],
   "rows": [
    [
     "20 mm",
     "10 × 5",
     "Ø3"
    ],
    [
     "30 mm",
     "10 × 5",
     "Ø3"
    ],
    [
     "40 mm",
     "10 × 5",
     "Ø3"
    ],
    [
     "50 mm",
     "10 × 5",
     "Ø3"
    ],
    [
     "60 mm",
     "10 × 5",
     "Ø3"
    ],
    [
     "80 mm",
     "10 × 5",
     "Ø3"
    ],
    [
     "100 mm",
     "10 × 5",
     "Ø3"
    ]
   ]
  }
 },
 "sheet_text": "Four-bar links: flat links with 20 to 100 mm hole centres — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/four-bar-links/  (CC BY 4.0)\nBasis: Flat links 10 wide × 5 thick, Ø3 holes at exact centres from 20 to 100 mm\nCatalog version: 2026-10-20\n\nSizes: see table below\n- Seven lengths: 20, 30, 40, 50, 60, 80 and 100 mm between hole centres.\n- Ø3 holes at both ends for Ø3 pins, so links pin to each other, to the bell cranks and to the Scotch yoke rod.\n- Builds crank-rockers, parallel motions, rocking beams and the Ross yoke linkage.\n\ncentres  width × thickness  holes\n20 mm  10 × 5  Ø3\n30 mm  10 × 5  Ø3\n40 mm  10 × 5  Ø3\n50 mm  10 × 5  Ø3\n60 mm  10 × 5  Ø3\n80 mm  10 × 5  Ø3\n100 mm  10 × 5  Ø3\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Wikipedia: Four-bar linkage — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Four-bar_linkage\n- Long Earth Society: Engine and rig builds on extrusion frames — web, video — LES site — https://longearthsociety.com/engineering/\n\nFree files (CC BY 4.0, Xem Studio; STEP + STL, 7 parts): https://xemstudio.com/files/hardware/four-bar-links/index.json\nAPI: https://xemstudio.com/api/geometry?object=four-bar-links\n",
 "sources": [
  {
   "publisher": "Wikipedia",
   "title": "Four-bar linkage",
   "url": "https://en.wikipedia.org/wiki/Four-bar_linkage",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text)",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Long Earth Society",
   "title": "Engine and rig builds on extrusion frames",
   "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": [
  "bell-cranks",
  "dowel-pins-metric",
  "ross-yoke-kit",
  "scotch-yoke",
  "pins-clevises-and-joints"
 ],
 "fits": [
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "bell-cranks",
     "why": "Ø3 arm holes"
    },
    {
     "slug": "scotch-yoke",
     "why": "Ø3 rod-end hole"
    },
    {
     "slug": "eccentric-and-strap",
     "why": "Ø3 strap eye"
    }
   ]
  },
  {
   "role": "Alternatives",
   "items": [
    {
     "slug": "ross-yoke-kit",
     "why": "solved Ross linkage for an alpha"
    }
   ]
  },
  {
   "role": "Also needed",
   "items": [
    {
     "slug": "dowel-pins-metric",
     "why": "Ø3 pins through the joints"
    }
   ]
  }
 ],
 "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": "end holes",
   "exact": "Ø3",
   "mates": "Ø3 pins (turn in them)",
   "fit": "run",
   "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": "Which lengths make a crank-rocker?",
   "a": "Grashof: shortest + longest ≤ the sum of the other two, with the shortest as the crank. For example a 20 crank, 60 coupler, 50 rocker and 60 ground."
  },
  {
   "q": "What pins go through the holes?",
   "a": "Ø3 pins, dowels or shafts; the holes are Ø3 exactly, so apply your fit to them."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "link-20",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/four-bar-links/link-20.step",
   "stl": "https://xemstudio.com/files/hardware/four-bar-links/link-20.stl",
   "note": "four-bar / rocker link, 20 mm centres, Ø3 holes, 10 wide × 5 thick"
  },
  {
   "file": "link-30",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/four-bar-links/link-30.step",
   "stl": "https://xemstudio.com/files/hardware/four-bar-links/link-30.stl",
   "note": "four-bar / rocker link, 30 mm centres, Ø3 holes, 10 wide × 5 thick"
  },
  {
   "file": "link-40",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/four-bar-links/link-40.step",
   "stl": "https://xemstudio.com/files/hardware/four-bar-links/link-40.stl",
   "note": "four-bar / rocker link, 40 mm centres, Ø3 holes, 10 wide × 5 thick"
  },
  {
   "file": "link-50",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/four-bar-links/link-50.step",
   "stl": "https://xemstudio.com/files/hardware/four-bar-links/link-50.stl",
   "note": "four-bar / rocker link, 50 mm centres, Ø3 holes, 10 wide × 5 thick"
  },
  {
   "file": "link-60",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/four-bar-links/link-60.step",
   "stl": "https://xemstudio.com/files/hardware/four-bar-links/link-60.stl",
   "note": "four-bar / rocker link, 60 mm centres, Ø3 holes, 10 wide × 5 thick"
  },
  {
   "file": "link-80",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/four-bar-links/link-80.step",
   "stl": "https://xemstudio.com/files/hardware/four-bar-links/link-80.stl",
   "note": "four-bar / rocker link, 80 mm centres, Ø3 holes, 10 wide × 5 thick"
  },
  {
   "file": "link-100",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/four-bar-links/link-100.step",
   "stl": "https://xemstudio.com/files/hardware/four-bar-links/link-100.stl",
   "note": "four-bar / rocker link, 100 mm centres, Ø3 holes, 10 wide × 5 thick"
  }
 ],
 "markdown": "https://xemstudio.com/objects/four-bar-links/index.md"
}