{
 "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": "spur-gear-pair-mechanism",
 "name": "Spur gear pair, module 1, 20 : 40 teeth (2 : 1)",
 "kind": "hardware",
 "category": "Mechanisms",
 "group": "Gears",
 "year": null,
 "question": "How do two spur gears change speed and direction?",
 "tags": [
  "mechanism",
  "gears",
  "kinematics",
  "507 mechanical movements"
 ],
 "aliases": [
  "spur gears",
  "gear pair",
  "gear ratio 2:1",
  "spur gear mesh",
  "par de engranajes rectos",
  "Stirnradpaar"
 ],
 "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/spur-gear-pair-mechanism/",
 "sheet_txt": "https://xemstudio.com/objects/spur-gear-pair-mechanism/sheet.txt",
 "sheet": {
  "basis": "Xem Studio design following Brown No. 24 (1868)",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "Two involute spur gears on parallel shafts: the speed ratio is the inverse tooth ratio (20 : 40 → output at half speed, double torque) and the shafts turn in opposite directions.",
   "Module 1, 20° pressure angle, centre distance m(N₁ + N₂)/2 = 30 mm exactly; teeth meet on the pitch line with no backlash drawn.",
   "Brown's figure 24 is the plain spur pair, the base of every gear train in the book.",
   "Parts (each has its own page): spur-gears-module-1.",
   "Brown's movement No. 24 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size."
  ],
  "table": {
   "columns": [
    "parameter",
    "value"
   ],
   "rows": [
    [
     "module",
     "1"
    ],
    [
     "teeth",
     "20 / 40"
    ],
    [
     "ratio",
     "2 : 1"
    ],
    [
     "centre distance",
     "30 mm"
    ],
    [
     "face width",
     "8 mm"
    ]
   ]
  }
 },
 "sheet_text": "Spur gear pair, module 1, 20 : 40 teeth (2 : 1) — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/spur-gear-pair-mechanism/  (CC BY 4.0)\nBasis: Xem Studio design following Brown No. 24 (1868)\nCatalog version: 2026-10-20\n\nSizes: see table below\n- Two involute spur gears on parallel shafts: the speed ratio is the inverse tooth ratio (20 : 40 → output at half speed, double torque) and the shafts turn in opposite directions.\n- Module 1, 20° pressure angle, centre distance m(N₁ + N₂)/2 = 30 mm exactly; teeth meet on the pitch line with no backlash drawn.\n- Brown's figure 24 is the plain spur pair, the base of every gear train in the book.\n- Parts (each has its own page): spur-gears-module-1.\n- Brown's movement No. 24 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.\n\nparameter  value\nmodule  1\nteeth  20 / 40\nratio  2 : 1\ncentre distance  30 mm\nface width  8 mm\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. 24: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_024.html\n\nFree files (CC BY 4.0, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/spur-gear-pair-mechanism/index.json\nAPI: https://xemstudio.com/api/geometry?object=spur-gear-pair-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. 24: figure, his text and an animation",
   "url": "https://507movements.com/mm_024.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": [
  "spur-gears-module-1"
 ],
 "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 do two spur gears change speed and direction?",
   "a": "Two involute spur gears on parallel shafts: the speed ratio is the inverse tooth ratio (20 : 40 → output at half speed, double torque) and the shafts turn in opposite directions."
  },
  {
   "q": "What is the centre distance of a 20 and 40 tooth module 1 pair?",
   "a": "30 mm: m × (20 + 40) / 2."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "spur-gear-pair-mechanism-assembly",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/spur-gear-pair-mechanism/spur-gear-pair-mechanism-assembly.step",
   "stl": "https://xemstudio.com/files/hardware/spur-gear-pair-mechanism/spur-gear-pair-mechanism-assembly.stl",
   "note": "Assembled mechanism, all parts placed at one pose (STEP keeps each part separate)"
  }
 ],
 "markdown": "https://xemstudio.com/objects/spur-gear-pair-mechanism/index.md"
}