{
  "version": "0.1",
  "nodes": {
    "1": { "id": 1, "name": "outer_cylinder", "op": {"type": "Cylinder", "radius": 15, "height": 40, "segments": 32} },
    "2": { "id": 2, "name": "inner_cylinder", "op": {"type": "Cylinder", "radius": 10, "height": 40, "segments": 32} },
    "3": { "id": 3, "name": "pipe", "op": {"type": "Difference", "left": 1, "right": 2} }
  },
  "materials": {},
  "part_materials": {},
  "roots": [{ "root": 3, "material": "default" }]
}