{
 "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": "parallel-ruler-crossed-arms-mechanism",
 "name": "Parallel ruler with crossed arms and slots",
 "kind": "hardware",
 "category": "Mechanisms",
 "group": "Linkages",
 "year": null,
 "question": "How does a parallel ruler stay parallel?",
 "tags": [
  "mechanism",
  "linkages",
  "kinematics",
  "507 mechanical movements"
 ],
 "aliases": [
  "parallel ruler",
  "navigation parallel rule",
  "drafting parallel ruler",
  "regla paralela",
  "Parallellineal"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": false,
 "free_files": 1,
 "url": "https://xemstudio.com/objects/parallel-ruler-crossed-arms-mechanism/",
 "sheet_txt": "https://xemstudio.com/objects/parallel-ruler-crossed-arms-mechanism/sheet.txt",
 "sheet": {
  "basis": "Xem Studio design following Brown No. 324 (1868)",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "Two straight-edges joined by two equal crossed arms pinned at their middles; each arm is pinned to one blade and slides in a slot of the other. The pinned ends are always one above the other, so the blades stay parallel and square to each other at any opening.",
   "Built from two 200 mm blades and two 80 mm centre-hole links: drawn open 40 mm; the slot lets it open from 0 to 55 mm.",
   "Brown's No. 324 (compound parallel ruler, crossed arms with slot-and-pin).",
   "Parts (each has its own page): parallel-ruler-blade-200, centre-hole-link-80, dowel-pins-metric.",
   "Brown's movement No. 324 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size."
  ],
  "table": {
   "columns": [
    "parameter",
    "value"
   ],
   "rows": [
    [
     "blades",
     "2 × 200 × 20 × 5 mm"
    ],
    [
     "arms",
     "2 × 80 mm, crossed at the middle"
    ],
    [
     "opening",
     "0–55 mm (drawn 40)"
    ]
   ]
  }
 },
 "sheet_text": "Parallel ruler with crossed arms and slots — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/parallel-ruler-crossed-arms-mechanism/  (CC BY 4.0)\nBasis: Xem Studio design following Brown No. 324 (1868)\nCatalog version: 2026-10-20\n\nSizes: see table below\n- Two straight-edges joined by two equal crossed arms pinned at their middles; each arm is pinned to one blade and slides in a slot of the other. The pinned ends are always one above the other, so the blades stay parallel and square to each other at any opening.\n- Built from two 200 mm blades and two 80 mm centre-hole links: drawn open 40 mm; the slot lets it open from 0 to 55 mm.\n- Brown's No. 324 (compound parallel ruler, crossed arms with slot-and-pin).\n- Parts (each has its own page): parallel-ruler-blade-200, centre-hole-link-80, dowel-pins-metric.\n- Brown's movement No. 324 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.\n\nparameter  value\nblades  2 × 200 × 20 × 5 mm\narms  2 × 80 mm, crossed at the middle\nopening  0–55 mm (drawn 40)\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Henry T. Brown (1868, public domain): Five Hundred and Seven Mechanical Movements — scan on archive.org — web — Publisher's page; dimensions are facts — https://archive.org/details/fivehundredseven00browiala\n- 507movements.com: Brown's movement No. 324: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_324.html\n\nFree files (CC BY 4.0, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/parallel-ruler-crossed-arms-mechanism/index.json\nAPI: https://xemstudio.com/api/geometry?object=parallel-ruler-crossed-arms-mechanism\n",
 "sources": [
  {
   "publisher": "Henry T. Brown (1868, public domain)",
   "title": "Five Hundred and Seven Mechanical Movements — scan on archive.org",
   "url": "https://archive.org/details/fivehundredseven00browiala",
   "formats": [
    "web"
   ],
   "license": "Publisher's page; dimensions are facts",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "507movements.com",
   "title": "Brown's movement No. 324: figure, his text and an animation",
   "url": "https://507movements.com/mm_324.html",
   "formats": [
    "web"
   ],
   "license": "Publisher's page; dimensions are facts",
   "license_verified": true,
   "hosted": false
  }
 ],
 "xem": {
  "status": "free-files",
  "sheet_free": true,
  "mesh_price_usd": null,
  "step_price_usd": null,
  "tolerance_mm": null
 },
 "related": [
  "parallel-ruler-blade-200",
  "centre-hole-link-80",
  "dowel-pins-metric"
 ],
 "fits": [],
 "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": [],
 "faq": [
  {
   "q": "How does a parallel ruler stay parallel?",
   "a": "Two straight-edges joined by two equal crossed arms pinned at their middles; each arm is pinned to one blade and slides in a slot of the other. The pinned ends are always one above the other, so the blades stay parallel and square to each other at any opening."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "parallel-ruler-crossed-arms-mechanism-assembly",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/parallel-ruler-crossed-arms-mechanism/parallel-ruler-crossed-arms-mechanism-assembly.step",
   "stl": "https://xemstudio.com/files/hardware/parallel-ruler-crossed-arms-mechanism/parallel-ruler-crossed-arms-mechanism-assembly.stl",
   "note": "Assembled mechanism, all parts placed at one pose (STEP keeps each part separate)"
  }
 ],
 "markdown": "https://xemstudio.com/objects/parallel-ruler-crossed-arms-mechanism/index.md"
}