"three-high" meaning in English

{
  "forms": [
    {
      "form": "three-highs",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "three-high (plural three-highs)",
      "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"
        },
        {
          "kind": "other",
          "name": "Pages with 1 entry",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with entries",
          "parents": [],
          "source": "w"
        }
      ],
      "examples": [
        {
          "ref": "1896, Engineering Review, volume 4, page 169:",
          "text": "For every section it is necessary to insert a special finishing roll in the stage lying next the large engine, while the three-highs in the other two stages contain the roughing rolls for all six profiles.",
          "type": "quote"
        }
      ],
      "glosses": [
        "A series of three rollers in a roller mill, stacked one above the other."
      ],
      "id": "en-three-high-en-noun-aB2DGKya",
      "links": [
        [
          "roller",
          "roller"
        ],
        [
          "roller mill",
          "roller mill"
        ]
      ]
    }
  ],
  "word": "three-high"
}

{
  "forms": [
    {
      "form": "three-highs",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "three-high (plural three-highs)",
      "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",
        "English terms with quotations",
        "Pages with 1 entry",
        "Pages with entries"
      ],
      "examples": [
        {
          "ref": "1896, Engineering Review, volume 4, page 169:",
          "text": "For every section it is necessary to insert a special finishing roll in the stage lying next the large engine, while the three-highs in the other two stages contain the roughing rolls for all six profiles.",
          "type": "quote"
        }
      ],
      "glosses": [
        "A series of three rollers in a roller mill, stacked one above the other."
      ],
      "links": [
        [
          "roller",
          "roller"
        ],
        [
          "roller mill",
          "roller mill"
        ]
      ]
    }
  ],
  "word": "three-high"
}