{
  "scope": "historical 4-front / 6-shell / 7-rear dictionary; exact edition and modern completeness unresolved",
  "letters": [
    {
      "position": "front",
      "code": "A",
      "construction": "Removable channel and cover"
    },
    {
      "position": "front",
      "code": "B",
      "construction": "Bonnet (integral cover)"
    },
    {
      "position": "front",
      "code": "C",
      "construction": "Integral with tubesheet; removable cover"
    },
    {
      "position": "front",
      "code": "D",
      "construction": "Special high-pressure closures"
    },
    {
      "position": "shell",
      "code": "E",
      "construction": "One-pass shell"
    },
    {
      "position": "shell",
      "code": "F",
      "construction": "Two-pass; longitudinal baffle"
    },
    {
      "position": "shell",
      "code": "G",
      "construction": "Split flow"
    },
    {
      "position": "shell",
      "code": "H",
      "construction": "Double split flow"
    },
    {
      "position": "shell",
      "code": "J",
      "construction": "Divided flow"
    },
    {
      "position": "shell",
      "code": "K",
      "construction": "Kettle-type reboiler"
    },
    {
      "position": "rear",
      "code": "L",
      "construction": "Fixed tubesheet, like A"
    },
    {
      "position": "rear",
      "code": "M",
      "construction": "Fixed tubesheet, like B"
    },
    {
      "position": "rear",
      "code": "N",
      "construction": "Fixed tubesheet, like C"
    },
    {
      "position": "rear",
      "code": "P",
      "construction": "Outside packed floating head"
    },
    {
      "position": "rear",
      "code": "S",
      "construction": "Floating head with backing device"
    },
    {
      "position": "rear",
      "code": "T",
      "construction": "Pull-through floating head"
    },
    {
      "position": "rear",
      "code": "U",
      "construction": "U-tube bundle"
    }
  ],
  "examples": [
    {
      "code": "AES",
      "parts": [
        "A",
        "E",
        "S"
      ],
      "access_questions": [
        "channel cover",
        "outer shell cover",
        "backing device release"
      ]
    },
    {
      "code": "AKU",
      "parts": [
        "A",
        "K",
        "U"
      ],
      "access_questions": [
        "channel cover",
        "U-tube bundle removal",
        "kettle internal regions"
      ]
    }
  ],
  "sketch_semantics": "sectional construction distinctions; no assembled-design certification"
}