{
 "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": "htd-power-pistons",
 "name": "HTD power pistons: Ø48.00 × 72 for the bored 2 in spool",
 "kind": "hardware",
 "category": "Stirling engines",
 "group": "Tri-clamp engine parts",
 "year": null,
 "question": "What piston goes in a bored 2 inch tri-clamp spool?",
 "tags": [
  "htd",
  "piston",
  "power piston",
  "stirling"
 ],
 "aliases": [
  "48 mm stirling piston",
  "tri clamp piston bored spool"
 ],
 "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/htd-power-pistons/",
 "sheet_txt": "https://xemstudio.com/objects/htd-power-pistons/sheet.txt",
 "sheet": {
  "basis": "Exact geometry at the finished bore Ø48.00",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "Ring-less: the seal is the fit. Two 8 lands carry it, 0.4 relief between them, 72 long (1.5 × bore) so it cannot cock. The crown faces the working space (down).",
   "The con-rod runs beside the axis (x 10.5..15.5) between two cheeks; the displacer rod passes up the centre tube (main piston) without touching the con-rod. The offset puts a small tilting moment on the piston, which the 72 length carries."
  ],
  "table": {
   "columns": [
    "part",
    "od_mm",
    "length_mm",
    "centre_bore_mm",
    "pin"
   ],
   "rows": [
    [
     "piston-48-rod6",
     48,
     72,
     6,
     "Ø5 at z 86, x 5..21"
    ]
   ]
  }
 },
 "sheet_text": "HTD power pistons: Ø48.00 × 72 for the bored 2 in spool — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/htd-power-pistons/  (CC BY 4.0)\nBasis: Exact geometry at the finished bore Ø48.00\nCatalog version: 2026-10-20\n\nSizes: see table below\n- Ring-less: the seal is the fit. Two 8 lands carry it, 0.4 relief between them, 72 long (1.5 × bore) so it cannot cock. The crown faces the working space (down).\n- The con-rod runs beside the axis (x 10.5..15.5) between two cheeks; the displacer rod passes up the centre tube (main piston) without touching the con-rod. The offset puts a small tilting moment on the piston, which the 72 length carries.\n\npart  od_mm  length_mm  centre_bore_mm  pin\npiston-48-rod6  48.0  72.0  6.0  Ø5 at z 86, x 5..21\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/htd-power-pistons/index.json\nAPI: https://xemstudio.com/api/geometry?object=htd-power-pistons\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": [
  "list-htd-10in",
  "htd-bored-power-spool",
  "htd-crank-linkage"
 ],
 "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": "OD",
   "exact": "Ø48.00, two 8 lands",
   "mates": "bored spool Ø48.00 (ring-less clearance seal)",
   "fit": "run",
   "files": "all"
  },
  {
   "feature": "centre bore",
   "exact": "Ø6 × 72",
   "mates": "displacer rod (also the bleed to the crankcase)",
   "fit": "run",
   "files": "piston-48-rod6"
  },
  {
   "feature": "pin bore",
   "exact": "Ø5 in both cheeks",
   "mates": "dowel-5x16",
   "fit": "press",
   "files": "all"
  },
  {
   "feature": "cheek gap",
   "exact": "6.0 (x 10..16)",
   "mates": "5 thick con-rod (0.5 each side)",
   "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 does the displacer rod get past the piston?",
   "a": "Through the piston's centre tube (Ø6 running fit, 72 long), which is also the bleed between working space and crankcase."
  }
 ],
 "files_license": null,
 "offers": [
  {
   "file": "piston-48-rod6",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "CC BY 4.0 (Xem Studio)",
   "step": "https://xemstudio.com/files/hardware/htd-power-pistons/piston-48-rod6.step",
   "stl": "https://xemstudio.com/files/hardware/htd-power-pistons/piston-48-rod6.stl",
   "note": "Ø48.00 × 72 power piston: two 8 lands, 0.4 relief, 8 crown, Ø14 centre tube with the Ø6 displacer-rod bore, cross bar and two cheeks with a Ø5 pin bore 14 above the skirt (con-rod at x 10.5..15.5)"
  }
 ],
 "markdown": "https://xemstudio.com/objects/htd-power-pistons/index.md"
}