{
 "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-ringbom-displacer-cap",
 "name": "Ringbom displacer cap for an 8 mm rod, 2 in shell displacer",
 "kind": "hardware",
 "category": "Hardware",
 "group": "Stirling & thermoacoustic",
 "year": null,
 "question": "How do I fit a Ringbom rod to a tri-clamp displacer?",
 "tags": [
  "ringbom",
  "displacer",
  "cap",
  "tri-clamp",
  "stirling",
  "long earth society"
 ],
 "aliases": [
  "ringbom displacer",
  "ringbom stirling rod",
  "free displacer cap"
 ],
 "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/tri-clamp-ringbom-displacer-cap/",
 "sheet_txt": "https://xemstudio.com/objects/tri-clamp-ringbom-displacer-cap/sheet.txt",
 "sheet": {
  "basis": "Shell spigot and flange as the displacer cap on this site (2 in shell Ø46 × 1 mm wall); Ø8 rod and M4 grub sizes are design values",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "Closes a 2 in shell displacer like the standard cap and holds an Ø8 rod instead of an Ø3 one. The rod is the Ringbom drive: its cross-section (50.3 mm²) times the gas pressure minus air pressure is the force that moves the free displacer.",
   "The rod's D-flat end goes in the Ø8 socket, 12 deep, and the M4 grub seats on the flat."
  ],
  "table": {
   "columns": [
    "part",
    "spigot_mm",
    "flange_mm",
    "boss_mm",
    "socket_mm"
   ],
   "rows": [
    [
     "ringbom-cap-2in-r8",
     "Ø44 × 3",
     "Ø46 × 1.5",
     "Ø16 × 14",
     "Ø8 × 12"
    ]
   ]
  }
 },
 "sheet_text": "Ringbom displacer cap for an 8 mm rod, 2 in shell displacer — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/tri-clamp-ringbom-displacer-cap/  (CC BY 4.0)\nBasis: Shell spigot and flange as the displacer cap on this site (2 in shell Ø46 × 1 mm wall); Ø8 rod and M4 grub sizes are design values\nCatalog version: 2026-10-20\n\nSizes: see table below\n- Closes a 2 in shell displacer like the standard cap and holds an Ø8 rod instead of an Ø3 one. The rod is the Ringbom drive: its cross-section (50.3 mm²) times the gas pressure minus air pressure is the force that moves the free displacer.\n- The rod's D-flat end goes in the Ø8 socket, 12 deep, and the M4 grub seats on the flat.\n\npart  spigot_mm  flange_mm  boss_mm  socket_mm\nringbom-cap-2in-r8  Ø44 × 3  Ø46 × 1.5  Ø16 × 14  Ø8 × 12\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\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, 1 parts): https://xemstudio.com/files/hardware/tri-clamp-ringbom-displacer-cap/index.json\nAPI: https://xemstudio.com/api/geometry?object=tri-clamp-ringbom-displacer-cap\n",
 "sources": [
  {
   "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-displacer",
  "tri-clamp-rd-gland-caps",
  "list-tri-clamp-rd-ringbom"
 ],
 "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": "spigot",
   "exact": "Ø44 × 3",
   "mates": "2 in shell displacer bore",
   "fit": "slide",
   "files": "all"
  },
  {
   "feature": "rod socket",
   "exact": "Ø8 × 12",
   "mates": "Ø8 rod D-flat end (M4 grub)",
   "fit": "slide",
   "files": "all"
  },
  {
   "feature": "grub hole",
   "exact": "Ø3.3",
   "mates": "M4 tap drill",
   "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 strong is the Ringbom push?",
   "a": "50.3 mm² × the pressure difference: 0.5 N per 10 kPa, enough to lift about 51 g per 10 kPa."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "ringbom-cap-2in-r8",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/tri-clamp-ringbom-displacer-cap/ringbom-cap-2in-r8.step",
   "stl": "https://xemstudio.com/files/hardware/tri-clamp-ringbom-displacer-cap/ringbom-cap-2in-r8.stl",
   "note": "Ringbom displacer cap: Ø44 × 3 spigot into a 2 in shell displacer, Ø46 × 1.5 flange, Ø16 boss to 18.5 with an Ø8 socket 12 deep and an M4 grub (Ø3.3)"
  }
 ],
 "markdown": "https://xemstudio.com/objects/tri-clamp-ringbom-displacer-cap/index.md"
}