{
  "operation": "insert",
  "input": {
    "units": "mm",
    "size_mm": [
      240,
      160,
      45
    ],
    "minimum_web_mm": 8,
    "minimum_floor_mm": 10,
    "cavities": [
      {
        "id": "instrument-envelope",
        "position_mm": [
          20,
          20
        ],
        "size_mm": [
          100,
          60,
          30
        ],
        "clearance_mm": 1.5
      },
      {
        "id": "accessory-envelope",
        "position_mm": [
          145,
          30
        ],
        "size_mm": [
          65,
          45,
          35
        ],
        "clearance_mm": 1
      }
    ]
  }
}