"Robertson screw" meaning in English

{
  "etymology_text": "From Canadian inventor P. L. Robertson (1879-1951).",
  "forms": [
    {
      "form": "Robertson screws",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "Robertson screw (plural Robertson screws)",
      "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"
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          "source": "w"
        },
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          "parents": [
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      ],
      "glosses": [
        "A type of screw having a square recess in the head."
      ],
      "id": "en-Robertson_screw-en-noun-UNHh29HL",
      "links": [
        [
          "square",
          "square"
        ],
        [
          "recess",
          "recess"
        ]
      ],
      "related": [
        {
          "word": "Robertson screwdriver"
        }
      ],
      "wikipedia": [
        "P. L. Robertson"
      ]
    }
  ],
  "word": "Robertson screw"
}

{
  "etymology_text": "From Canadian inventor P. L. Robertson (1879-1951).",
  "forms": [
    {
      "form": "Robertson screws",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "Robertson screw (plural Robertson screws)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "related": [
    {
      "word": "Robertson screwdriver"
    }
  ],
  "senses": [
    {
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English entries with language name categories using raw markup",
        "English eponyms",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English terms with non-redundant non-automated sortkeys"
      ],
      "glosses": [
        "A type of screw having a square recess in the head."
      ],
      "links": [
        [
          "square",
          "square"
        ],
        [
          "recess",
          "recess"
        ]
      ],
      "wikipedia": [
        "P. L. Robertson"
      ]
    }
  ],
  "word": "Robertson screw"
}