{
 "version": "2026-10-20",
 "license": "Dimension sheets: CC BY 4.0. Standard and published-size files: CC BY 4.0. Xem Studio's own designs (files_license = Xem Studio Design License): free to use and sell things from, not to redistribute as files — https://xemstudio.com/license/. Other publishers' files: their own license, linked beside them.",
 "slug": "lifting-tongs-mechanism",
 "name": "Lifting tongs: load-tightened scissor grip",
 "kind": "hardware",
 "category": "Mechanisms",
 "group": "Linkages",
 "year": null,
 "question": "Why do lifting tongs grip harder with a heavier load?",
 "tags": [
  "mechanism",
  "linkages",
  "kinematics",
  "507 mechanical movements"
 ],
 "aliases": [
  "lifting tongs",
  "stone tongs",
  "scissor tongs",
  "self-tightening grab",
  "tenazas de elevación",
  "Hebezange"
 ],
 "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/lifting-tongs-mechanism/",
 "sheet_txt": "https://xemstudio.com/objects/lifting-tongs-mechanism/sheet.txt",
 "sheet": {
  "basis": "Xem Studio design following Brown No. 494 (1868)",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "Two arms crossed on a pivot, their upper ends drawn together by two equal links meeting at a shackle: the hoist pulls the shackle up, the links pull the arm tops inwards, and the feet below the pivot close on the load. The grip is proportional to the pull, so the heavier the load the tighter it is held.",
   "Drawn gripping a 40 mm block: arms crossed at ±22.02°, link holes 60 mm above and feet 80 mm below the pivot, 40 mm links to the shackle pin 88.69 mm above the pivot.",
   "Brown's No. 494 (lifting tongs with a shackle and links); ice tongs, log tongs and crane grabs.",
   "Parts (each has its own page): lifting-tong-arm-140-foot, tongs-shackle-link-50, load-block-40, four-bar-links, dowel-pins-metric.",
   "Brown's movement No. 494 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size."
  ],
  "table": {
   "columns": [
    "parameter",
    "value"
   ],
   "rows": [
    [
     "arms",
     "2, crossed, 60 / 80 mm"
    ],
    [
     "links",
     "2 × 40 mm"
    ],
    [
     "load drawn",
     "40 mm block"
    ],
    [
     "arm angle",
     "±22.02°"
    ]
   ]
  }
 },
 "sheet_text": "Lifting tongs: load-tightened scissor grip — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/lifting-tongs-mechanism/  (sheet CC BY 4.0; files Xem Studio Design License, https://xemstudio.com/license/)\nBasis: Xem Studio design following Brown No. 494 (1868)\nCatalog version: 2026-10-20\n\nSizes: see table below\n- Two arms crossed on a pivot, their upper ends drawn together by two equal links meeting at a shackle: the hoist pulls the shackle up, the links pull the arm tops inwards, and the feet below the pivot close on the load. The grip is proportional to the pull, so the heavier the load the tighter it is held.\n- Drawn gripping a 40 mm block: arms crossed at ±22.02°, link holes 60 mm above and feet 80 mm below the pivot, 40 mm links to the shackle pin 88.69 mm above the pivot.\n- Brown's No. 494 (lifting tongs with a shackle and links); ice tongs, log tongs and crane grabs.\n- Parts (each has its own page): lifting-tong-arm-140-foot, tongs-shackle-link-50, load-block-40, four-bar-links, dowel-pins-metric.\n- Brown's movement No. 494 (1868) shows it; this model is a Xem Studio design following his figure, every part at true size.\n\nparameter  value\narms  2, crossed, 60 / 80 mm\nlinks  2 × 40 mm\nload drawn  40 mm block\narm angle  ±22.02°\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. 494: figure, his text and an animation — web — Publisher's page; dimensions are facts — https://507movements.com/mm_494.html\n\nFree files (Xem Studio Design License, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/lifting-tongs-mechanism/index.json\nAPI: https://xemstudio.com/api/geometry?object=lifting-tongs-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. 494: figure, his text and an animation",
   "url": "https://507movements.com/mm_494.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": [
  "lifting-tong-arm-140-foot",
  "tongs-shackle-link-50",
  "load-block-40",
  "four-bar-links",
  "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": "Why do lifting tongs grip harder with a heavier load?",
   "a": "Two arms crossed on a pivot, their upper ends drawn together by two equal links meeting at a shackle: the hoist pulls the shackle up, the links pull the arm tops inwards, and the feet below the pivot close on the load. The grip is proportional to the pull, so the heavier the load the tighter it is held."
  }
 ],
 "files_license": {
  "name": "Xem Studio Design License",
  "holder": "Xem Studio",
  "url": "https://xemstudio.com/license/",
  "note": "Xem Studio's own design: free to use, print, modify and sell things made from it; not to be republished or redistributed as files."
 },
 "offers": [
  {
   "file": "lifting-tongs-mechanism-assembly",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "Xem Studio Design License",
   "step": "https://xemstudio.com/files/hardware/lifting-tongs-mechanism/lifting-tongs-mechanism-assembly.step",
   "stl": "https://xemstudio.com/files/hardware/lifting-tongs-mechanism/lifting-tongs-mechanism-assembly.stl",
   "note": "Assembled mechanism, all parts placed at one pose (STEP keeps each part separate)"
  }
 ],
 "markdown": "https://xemstudio.com/objects/lifting-tongs-mechanism/index.md"
}