{
 "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": "tri-clamp-diaphragm-disc",
 "name": "Tri-clamp diaphragm centre disc and backing disc: 1.5 and 2 in",
 "kind": "hardware",
 "category": "Hardware",
 "group": "Stirling & thermoacoustic",
 "year": null,
 "question": "How do I attach a rod to a diaphragm membrane?",
 "tags": [
  "disc",
  "diaphragm",
  "rod",
  "tri-clamp",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "diaphragm centre disc",
  "attach rod to diaphragm",
  "diaphragm clamp plate",
  "stirling diaphragm rod"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": true,
 "free_files": 4,
 "url": "https://xemstudio.com/objects/tri-clamp-diaphragm-disc/",
 "sheet_txt": "https://xemstudio.com/objects/tri-clamp-diaphragm-disc/sheet.txt",
 "sheet": {
  "basis": "Design values: disc diameter chosen so the free membrane span gives the design stroke; M2 screws (ISO 4762) and ISO 273 medium clearance holes",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "The centre disc sits on the head side of the membrane and carries the rod: a Ø8 × 8 boss with a Ø3 socket (floor 1 mm above the membrane side) held by an M3 grub in a Ø2.5 radial hole 4 mm up the boss. The backing disc sits on the gas side.",
   "Three M2 × 8 screws go from the gas side through the backing disc, the membrane and the centre disc into M2 nuts on top; the nuts sit flat-side to the boss.",
   "Disc Ø17 (1.5 in) and Ø20 (2 in): smaller discs leave more free span, so more stroke at the same membrane stretch."
  ],
  "table": {
   "columns": [
    "size_in",
    "disc_dia_mm",
    "disc_t_mm",
    "backing_t_mm",
    "boss_dia_mm",
    "boss_h_mm",
    "screw_circle_mm",
    "screws"
   ],
   "rows": [
    [
     "2",
     20,
     3,
     2,
     8,
     8,
     13,
     "3 × M2 × 8 + nuts"
    ],
    [
     "1.5",
     17,
     3,
     2,
     8,
     8,
     12,
     "3 × M2 × 8 + nuts"
    ]
   ]
  }
 },
 "sheet_text": "Tri-clamp diaphragm centre disc and backing disc: 1.5 and 2 in — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/tri-clamp-diaphragm-disc/  (CC BY 4.0)\nBasis: Design values: disc diameter chosen so the free membrane span gives the design stroke; M2 screws (ISO 4762) and ISO 273 medium clearance holes\nCatalog version: 2026-10-20\n\nSizes: see table below\n- The centre disc sits on the head side of the membrane and carries the rod: a Ø8 × 8 boss with a Ø3 socket (floor 1 mm above the membrane side) held by an M3 grub in a Ø2.5 radial hole 4 mm up the boss. The backing disc sits on the gas side.\n- Three M2 × 8 screws go from the gas side through the backing disc, the membrane and the centre disc into M2 nuts on top; the nuts sit flat-side to the boss.\n- Disc Ø17 (1.5 in) and Ø20 (2 in): smaller discs leave more free span, so more stroke at the same membrane stretch.\n\nsize_in  disc_dia_mm  disc_t_mm  backing_t_mm  boss_dia_mm  boss_h_mm  screw_circle_mm  screws\n2  20.0  3.0  2.0  8.0  8.0  13.0  3 × M2 × 8 + nuts\n1.5  17.0  3.0  2.0  8.0  8.0  12.0  3 × M2 × 8 + nuts\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- ISO: ISO 273 clearance holes for bolts and screws (fine / medium / coarse) — standard — dimensions are facts [verify license at link] — https://www.iso.org/standard/4196.html\n- Long Earth Society: Engine builds — web, video — LES site — https://longearthsociety.com/engineering/\n\nFree files (CC BY 4.0, Xem Studio; STEP + STL, 4 parts): https://xemstudio.com/files/hardware/tri-clamp-diaphragm-disc/index.json\nAPI: https://xemstudio.com/api/geometry?object=tri-clamp-diaphragm-disc\n",
 "sources": [
  {
   "publisher": "ISO",
   "title": "ISO 273 clearance holes for bolts and screws (fine / medium / coarse)",
   "url": "https://www.iso.org/standard/4196.html",
   "formats": [
    "standard"
   ],
   "license": "dimensions are facts",
   "license_verified": false,
   "hosted": false
  },
  {
   "publisher": "Long Earth Society",
   "title": "Engine 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": [
  "tri-clamp-diaphragm-head",
  "tri-clamp-diaphragm-membrane",
  "socket-head-cap-screws-metric",
  "hex-nuts-metric",
  "set-screws-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": [
  {
   "feature": "rod socket",
   "exact": "Ø3 × 10",
   "mates": "Ø3 rod (M3 grub)",
   "fit": "slide",
   "files": "diaphragm-disc-"
  },
  {
   "feature": "grub hole",
   "exact": "Ø2.5",
   "mates": "M3 tap drill",
   "fit": "designed",
   "files": "diaphragm-disc-"
  },
  {
   "feature": "screw holes",
   "exact": "3 × Ø2.4",
   "mates": "M2 clearance (ISO 273 medium)",
   "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": "How is the rod held?",
   "a": "In the Ø3 socket of the centre-disc boss by an M3 grub screw."
  },
  {
   "q": "Which side does each disc go?",
   "a": "Centre disc (with the boss) on the head side, backing disc on the gas side; the screw heads are on the gas side."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "diaphragm-disc-2in",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/tri-clamp-diaphragm-disc/diaphragm-disc-2in.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-diaphragm-disc/diaphragm-disc-2in.stl",
   "note": "2 in centre disc Ø20 × 3, rod boss Ø8 × 8 with Ø3 socket and Ø2.5 grub hole (M3 tap drill), 3 × Ø2.4 on Ø13"
  },
  {
   "file": "diaphragm-backing-2in",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/tri-clamp-diaphragm-disc/diaphragm-backing-2in.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-diaphragm-disc/diaphragm-backing-2in.stl",
   "note": "2 in backing disc Ø20 × 2, 3 × Ø2.4 on Ø13 (gas side of the membrane)"
  },
  {
   "file": "diaphragm-disc-1.5in",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/tri-clamp-diaphragm-disc/diaphragm-disc-1.5in.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-diaphragm-disc/diaphragm-disc-1.5in.stl",
   "note": "1.5 in centre disc Ø17 × 3, rod boss Ø8 × 8 with Ø3 socket and Ø2.5 grub hole (M3 tap drill), 3 × Ø2.4 on Ø12"
  },
  {
   "file": "diaphragm-backing-1.5in",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/tri-clamp-diaphragm-disc/diaphragm-backing-1.5in.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-diaphragm-disc/diaphragm-backing-1.5in.stl",
   "note": "1.5 in backing disc Ø17 × 2, 3 × Ø2.4 on Ø12 (gas side of the membrane)"
  }
 ],
 "markdown": "https://xemstudio.com/objects/tri-clamp-diaphragm-disc/index.md"
}