"tin knocker" meaning in English

{
  "forms": [
    {
      "form": "tin knockers",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "tin knocker (plural tin knockers)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        }
      ],
      "examples": [
        {
          "text": "We can't hang drywall in here until the tin knockers are done."
        }
      ],
      "glosses": [
        "A sheet metal worker, especially one who works with HVAC ductwork."
      ],
      "id": "en-tin_knocker-en-noun-oj~tkBje",
      "links": [
        [
          "sheet metal",
          "sheet metal"
        ],
        [
          "HVAC",
          "HVAC"
        ],
        [
          "ductwork",
          "ductwork"
        ]
      ]
    }
  ],
  "word": "tin knocker"
}

{
  "forms": [
    {
      "form": "tin knockers",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "tin knocker (plural tin knockers)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns"
      ],
      "examples": [
        {
          "text": "We can't hang drywall in here until the tin knockers are done."
        }
      ],
      "glosses": [
        "A sheet metal worker, especially one who works with HVAC ductwork."
      ],
      "links": [
        [
          "sheet metal",
          "sheet metal"
        ],
        [
          "HVAC",
          "HVAC"
        ],
        [
          "ductwork",
          "ductwork"
        ]
      ]
    }
  ],
  "word": "tin knocker"
}