{
 "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": "m42-screw-mount",
 "name": "M42 screw mount (M42 × 1): 45.46 mm flange, thread rings",
 "kind": "standard",
 "category": "Cameras & lenses",
 "group": "Lens mounts & filter threads",
 "year": null,
 "question": "What is the M42 screw mount flange focal distance?",
 "tags": [
  "lens mount",
  "camera",
  "lens",
  "mount",
  "adapter",
  "flange distance",
  "standard"
 ],
 "aliases": [
  "m42 thread pitch",
  "m42x1 thread",
  "m42 flange distance",
  "praktica screw mount",
  "pentax screw mount",
  "m42 adapter stl"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": false,
 "free_files": 2,
 "url": "https://xemstudio.com/objects/m42-screw-mount/",
 "sheet_txt": "https://xemstudio.com/objects/m42-screw-mount/sheet.txt",
 "sheet": {
  "basis": "Published numbers only (sources per row); thread drawn at the ISO 68-1 basic profile",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "Flange focal distance is the distance from the mount's reference face to the image plane; adapters and extension tubes must add exactly the difference between two mounts' flange distances to keep infinity focus.",
   "The lens carries the male M42 × 1 thread; the camera body the female one.",
   "Not the same as the T-mount (M42 × 0.75): the two look alike but the pitches differ and they do not screw together."
  ],
  "table": {
   "columns": [
    "parameter",
    "value",
    "from"
   ],
   "rows": [
    [
     "flange focal distance",
     "45.46 mm",
     "Flange focal distance table"
    ],
    [
     "throat / inner diameter",
     "not published in a source I could verify (left out)",
     "—"
    ],
    [
     "thread",
     "M42 × 1",
     "standard"
    ],
    [
     "major Ø D",
     "42.000 mm",
     "standard"
    ],
    [
     "pitch P",
     "1 mm",
     "standard"
    ],
    [
     "pitch Ø D2 (basic)",
     "41.350 mm",
     "ISO 68-1 basic profile"
    ],
    [
     "minor Ø D1 (basic)",
     "40.917 mm",
     "ISO 68-1 basic profile"
    ],
    [
     "files",
     "male and female ring sections, 8 turns, basic profile",
     "—"
    ]
   ]
  }
 },
 "sheet_text": "M42 screw mount (M42 × 1): 45.46 mm flange, thread rings — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/m42-screw-mount/  (sheet CC BY 4.0)\nBasis: Published numbers only (sources per row); thread drawn at the ISO 68-1 basic profile\nCatalog version: 2026-10-20\n\nSizes: see table below\n- Flange focal distance is the distance from the mount's reference face to the image plane; adapters and extension tubes must add exactly the difference between two mounts' flange distances to keep infinity focus.\n- The lens carries the male M42 × 1 thread; the camera body the female one.\n- Not the same as the T-mount (M42 × 0.75): the two look alike but the pitches differ and they do not screw together.\n\nparameter  value  from\nflange focal distance  45.46 mm  Flange focal distance table\nthroat / inner diameter  not published in a source I could verify (left out)  —\nthread  M42 × 1  standard\nmajor Ø D  42.000 mm  standard\npitch P  1 mm  standard\npitch Ø D2 (basic)  41.350 mm  ISO 68-1 basic profile\nminor Ø D1 (basic)  40.917 mm  ISO 68-1 basic profile\nfiles  male and female ring sections, 8 turns, basic profile  —\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Wikipedia: Flange focal distance (table of mounts) — web — CC BY-SA 4.0 (text); dimensions are facts — https://en.wikipedia.org/wiki/Flange_focal_distance\n- Bureau of Indian Standards (via Public.Resource.Org): IS 4218 (Part 1):2001 ISO general purpose metric screw threads, basic profile (identical with ISO 68-1:1998): H = 0.866025404 P, 5H/8 = 0.541265877 P, 3H/8 = 0.324759526 P — web — Public.Resource.Org (public law); dimensions are facts — https://law.resource.org/pub/in/bis/S01/is.4218.1.2001.pdf\n- ISO: ISO 68-1:1998 ISO general purpose screw threads — Basic profile — Part 1: Metric screw threads — web — Publisher's page; dimensions are facts — https://www.iso.org/standard/3707.html\n\nFree files (CC BY 4.0, Xem Studio; STEP + STL, 2 parts): https://xemstudio.com/files/hardware/m42-screw-mount/index.json\nAPI: https://xemstudio.com/api/geometry?object=m42-screw-mount\n",
 "sources": [
  {
   "publisher": "Wikipedia",
   "title": "Flange focal distance (table of mounts)",
   "url": "https://en.wikipedia.org/wiki/Flange_focal_distance",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text); dimensions are facts",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Bureau of Indian Standards (via Public.Resource.Org)",
   "title": "IS 4218 (Part 1):2001 ISO general purpose metric screw threads, basic profile (identical with ISO 68-1:1998): H = 0.866025404 P, 5H/8 = 0.541265877 P, 3H/8 = 0.324759526 P",
   "url": "https://law.resource.org/pub/in/bis/S01/is.4218.1.2001.pdf",
   "formats": [
    "web"
   ],
   "license": "Public.Resource.Org (public law); dimensions are facts",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "ISO",
   "title": "ISO 68-1:1998 ISO general purpose screw threads — Basic profile — Part 1: Metric screw threads",
   "url": "https://www.iso.org/standard/3707.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": [
  "t-mount-t2",
  "canon-ef-mount",
  "nikon-f-mount",
  "lens-filter-threads"
 ],
 "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": "What thread is M42?",
   "a": "M42 × 1 (42 mm, 1 mm pitch), 45.46 mm flange focal distance."
  },
  {
   "q": "Does an M42 lens fit a T-mount?",
   "a": "No: T-mount is M42 × 0.75, a different pitch."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "m42x1-male-ring",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/m42-screw-mount/m42x1-male-ring.step",
   "stl": "https://xemstudio.com/files/hardware/m42-screw-mount/m42x1-male-ring.stl",
   "note": "M42 × 1 lens mount external thread ring section: ISO 68-1 basic profile, major Ø42, pitch Ø41.350, minor Ø40.917, pitch 1; 8 long (8 turns), bore Ø36.917 (wall is a design choice); exact nominal, no tolerance"
  },
  {
   "file": "m42x1-female-ring",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/m42-screw-mount/m42x1-female-ring.step",
   "stl": "https://xemstudio.com/files/hardware/m42-screw-mount/m42x1-female-ring.stl",
   "note": "M42 × 1 lens mount internal thread ring section: ISO 68-1 basic profile, minor Ø40.917, pitch Ø41.350, major Ø42, pitch 1; 8 long (8 turns), outside Ø46 (design choice); exact nominal, no tolerance"
  }
 ],
 "markdown": "https://xemstudio.com/objects/m42-screw-mount/index.md"
}