{
 "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": "nut-trap-gauge",
 "name": "Nut-trap gauge: M3 5.5 / 5.7 / 5.9 AF and M4 7.0 / 7.2 / 7.4 AF",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Generators & instruments",
 "year": null,
 "question": "What nut-trap size does my 3D printer need for M3 and M4 nuts?",
 "tags": [
  "calibration",
  "gauge",
  "nut trap",
  "tolerance",
  "test print",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "nut trap tolerance",
  "m3 nut trap size",
  "hex nut pocket test print",
  "captive nut calibration",
  "m4 nut trap"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": true,
 "free_files": 1,
 "url": "https://xemstudio.com/objects/nut-trap-gauge/",
 "sheet_txt": "https://xemstudio.com/objects/nut-trap-gauge/sheet.txt",
 "sheet": {
  "basis": "Hex traps stepped from the ISO 4032 across-flats (M3 5.5, M4 7.0) in 0.2 mm steps",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "Every file on this site is drawn at exact size with no printing allowance; this gauge steps through sizes around the nominal so you can measure the allowance your process needs for one fit class, then apply it only to the features each object lists under Mating features.",
   "The gauge is an 80 × 24 × 5 mm plate with six hex traps on 13 mm pitch: M3 at 5.5, 5.7, 5.9 AF, 2.7 deep, and M4 at 7.0, 7.2, 7.4 AF, 3.5 deep.",
   "Press an M3 or M4 hex nut into each trap: the trap that holds it snug, minus 5.5 or 7.0, is your nut-trap allowance."
  ],
  "table": {
   "columns": [
    "trap",
    "af_mm",
    "depth_mm"
   ],
   "rows": [
    [
     "M3",
     "5.5 / 5.7 / 5.9",
     2.7
    ],
    [
     "M4",
     "7.0 / 7.2 / 7.4",
     3.5
    ]
   ]
  }
 },
 "sheet_text": "Nut-trap gauge: M3 5.5 / 5.7 / 5.9 AF and M4 7.0 / 7.2 / 7.4 AF — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/nut-trap-gauge/  (CC BY 4.0)\nBasis: Hex traps stepped from the ISO 4032 across-flats (M3 5.5, M4 7.0) in 0.2 mm steps\nCatalog version: 2026-10-20\n\nSizes: see table below\n- Every file on this site is drawn at exact size with no printing allowance; this gauge steps through sizes around the nominal so you can measure the allowance your process needs for one fit class, then apply it only to the features each object lists under Mating features.\n- The gauge is an 80 × 24 × 5 mm plate with six hex traps on 13 mm pitch: M3 at 5.5, 5.7, 5.9 AF, 2.7 deep, and M4 at 7.0, 7.2, 7.4 AF, 3.5 deep.\n- Press an M3 or M4 hex nut into each trap: the trap that holds it snug, minus 5.5 or 7.0, is your nut-trap allowance.\n\ntrap  af_mm  depth_mm\nM3  5.5 / 5.7 / 5.9  2.7\nM4  7.0 / 7.2 / 7.4  3.5\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- Wikipedia: Engineering tolerance — web — CC BY-SA 4.0 (text) — https://en.wikipedia.org/wiki/Engineering_tolerance\n- Prusa: Knowledge base: XY size compensation — web — Prusa KB [verify license at link] — https://help.prusa3d.com/article/xy-size-compensation_125045\n- Long Earth Society: Engine and rig builds — web, video — LES site — https://longearthsociety.com/engineering/\n\nFree files (CC BY 4.0, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/nut-trap-gauge/index.json\nAPI: https://xemstudio.com/api/geometry?object=nut-trap-gauge\n",
 "sources": [
  {
   "publisher": "Wikipedia",
   "title": "Engineering tolerance",
   "url": "https://en.wikipedia.org/wiki/Engineering_tolerance",
   "formats": [
    "web"
   ],
   "license": "CC BY-SA 4.0 (text)",
   "license_verified": true,
   "hosted": false
  },
  {
   "publisher": "Prusa",
   "title": "Knowledge base: XY size compensation",
   "url": "https://help.prusa3d.com/article/xy-size-compensation_125045",
   "formats": [
    "web"
   ],
   "license": "Prusa KB",
   "license_verified": false,
   "hosted": false
  },
  {
   "publisher": "Long Earth Society",
   "title": "Engine and rig builds",
   "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": [
  "hex-nuts-metric",
  "hole-gauges",
  "nyloc-nuts-metric"
 ],
 "fits": [
  {
   "role": "Connects to",
   "items": [
    {
     "slug": "hex-nuts-metric",
     "why": "M3 (5.5 AF) and M4 (7.0 AF) nuts pressed into the traps"
    }
   ]
  },
  {
   "role": "Also needed",
   "items": [
    {
     "slug": "hole-gauges",
     "why": "the screw-hole allowance"
    }
   ]
  }
 ],
 "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": "gauge sizes",
   "exact": "stepped around nominal",
   "mates": "the true pin, nut, bearing or extrusion slot being tested",
   "fit": "designed",
   "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": "What size nut trap for an M3 nut?",
   "a": "The nut is 5.5 mm across flats; print this gauge and the trap that holds it snug, minus 5.5, is your allowance."
  },
  {
   "q": "How deep are the traps?",
   "a": "2.7 mm for M3 and 3.5 mm for M4."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "nut-trap-gauge-m3-m4",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/printer-calibration-coupons/nut-trap-gauge-m3-m4.step",
   "stl": "https://xemstudio.com/files/hardware/printer-calibration-coupons/nut-trap-gauge-m3-m4.stl",
   "note": "nut-trap gauge: M3 at 5.5/5.7/5.9 AF, M4 at 7.0/7.2/7.4"
  }
 ],
 "markdown": "https://xemstudio.com/objects/nut-trap-gauge/index.md"
}