"6H" meaning in English

{
  "forms": [
    {
      "form": "6Hs",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "-",
        "2": "s"
      },
      "expansion": "6H (usually uncountable, plural 6Hs)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "_dis": "80 20",
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w+disamb"
        },
        {
          "_dis": "85 15",
          "kind": "other",
          "name": "Pages with 1 entry",
          "parents": [],
          "source": "w+disamb"
        },
        {
          "_dis": "91 9",
          "kind": "other",
          "name": "Pages with entries",
          "parents": [],
          "source": "w+disamb"
        }
      ],
      "glosses": [
        "A grade of pencil with lead that makes lighter marks than a pencil grade 5H; a pencil with extremely hard lead."
      ],
      "id": "en-6H-en-noun-UusahaVq",
      "links": [
        [
          "5H",
          "5H"
        ]
      ],
      "raw_glosses": [
        "(British English) A grade of pencil with lead that makes lighter marks than a pencil grade 5H; a pencil with extremely hard lead."
      ],
      "tags": [
        "British",
        "English",
        "uncountable",
        "usually"
      ]
    },
    {
      "glosses": [
        "A pencil of grade 6H."
      ],
      "id": "en-6H-en-noun-NbuiN5yW",
      "tags": [
        "uncountable",
        "usually"
      ]
    }
  ],
  "word": "6H"
}

{
  "categories": [
    "English countable nouns",
    "English entries with incorrect language header",
    "English lemmas",
    "English nouns",
    "English terms spelled with numbers",
    "English uncountable nouns",
    "English words without vowels",
    "Pages with 1 entry",
    "Pages with entries"
  ],
  "forms": [
    {
      "form": "6Hs",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "-",
        "2": "s"
      },
      "expansion": "6H (usually uncountable, plural 6Hs)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "glosses": [
        "A grade of pencil with lead that makes lighter marks than a pencil grade 5H; a pencil with extremely hard lead."
      ],
      "links": [
        [
          "5H",
          "5H"
        ]
      ],
      "raw_glosses": [
        "(British English) A grade of pencil with lead that makes lighter marks than a pencil grade 5H; a pencil with extremely hard lead."
      ],
      "tags": [
        "British",
        "English",
        "uncountable",
        "usually"
      ]
    },
    {
      "glosses": [
        "A pencil of grade 6H."
      ],
      "tags": [
        "uncountable",
        "usually"
      ]
    }
  ],
  "word": "6H"
}