{
  "units": "mm",
  "status": "Exploded bench comparison; not measured from the fitted car.",
  "placement": "Display stations along local +X only, with deliberate gaps. No engine registration, installed lengths or service travel.",
  "parts_source": "https://www.spridgets.de/downloads/Parts-1977.pdf#page=61",
  "parts_plate": "MB0699, printed 107-B85/B86, items 12\u201315; one of each.",
  "workshop_source": "https://www.spridgets.de/downloads/Midget%201500%20WH%20Teil%203.pdf#page=11",
  "workshop_scope": "Engine\u2014U.K. Specification, printed page 84, operation 12.60.56. Fitted North American specification and actual parts remain unverified.",
  "documentary_dimensions_mm": {
    "spring_free_length": 38.8,
    "replacement_washer_nominal_inside_diameter": 14.0
  },
  "spring_length_basis": "Use the printed metric 38.8 mm, alongside the rounded 1.53-inch manual value. This is free length, not installed length, preload, rate or relief pressure.",
  "washer_source": "https://rimmerbros.com/Item--i-6K433",
  "estimated_dimensions_mm": {
    "piston_head_diameter": 10,
    "piston_head_thickness": 2,
    "piston_stem_diameter": 4,
    "piston_stem_length": 30,
    "spring_wire_diameter": 1,
    "spring_mean_diameter": 7.5,
    "washer_outside_diameter": 20,
    "washer_thickness": 1.5,
    "plug_across_flats": 19,
    "plug_hex_length": 21,
    "plug_unthreaded_shank_diameter": 13.6,
    "plug_shank_length": 10,
    "plug_blind_bore_diameter": 9,
    "plug_blind_bore_depth": 25
  },
  "estimated_spring_turns": 12,
  "shape_references": {
    "piston": "https://rimmerbros.com/Item--i-132107",
    "spring": "https://rimmerbros.com/Item--i-131535",
    "plug": "https://rimmerbros.com/Item--i-107246"
  },
  "limits": "Head/stem piston, helical spring, annular washer and long hollow hex plug are recognition shapes. Thread form and pitch, spring end treatment and calibration, seat, passages, sealing, fitted variants, tool fit, torque and access are not reconstructed. Do not insert these bench coordinates into the engine or use this STEP as a replacement-part drawing.",
  "part_names": [
    "piston_132107_shape_provisional",
    "spring_131535_UK_free_length_38_8mm_profile_provisional",
    "washer_6K433_replacement_14mm_ID_other_sizes_provisional",
    "plug_107246_unthreaded_recognition_shape_provisional"
  ],
  "model_envelopes_mm": {
    "piston_132107_shape_provisional": {
      "x": 32.0,
      "y": 10.0,
      "z": 10.0
    },
    "spring_131535_UK_free_length_38_8mm_profile_provisional": {
      "x": 38.799999999996125,
      "y": 8.500002627536205,
      "z": 8.499994472960683
    },
    "washer_6K433_replacement_14mm_ID_other_sizes_provisional": {
      "x": 1.5,
      "y": 20.0,
      "z": 20.0
    },
    "plug_107246_unthreaded_recognition_shape_provisional": {
      "x": 31.0,
      "y": 21.93931022920578,
      "z": 19.000000000000007
    }
  }
}