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EQUITY - Ownership of shares (Details) - shares | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
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Capital |  |  |
Number of shares held | 1,719,658,728 | 1,719,658,728 | 1,719,658,728
Shares Issued, Percentage | 100.00% | 100.00% | 100.00%
Metalurgica Gerdau S.A. |  |  |
Capital |  |  |
Number of shares held | 653,368,823 | 653,370,032 | 652,519,280
Shares Issued, Percentage | 38.00% | 38.00% | 37.90%
Brazilian institutional investors |  |  |
Capital |  |  |
Number of shares held | 226,456,754 | 155,482,209 | 134,604,327
Shares Issued, Percentage | 13.20% | 9.00% | 7.80%
Foreign institutional investors |  |  |
Capital |  |  |
Number of shares held | 415,223,778 | 715,363,943 | 716,775,213
Shares Issued, Percentage | 24.10% | 41.60% | 41.80%
Other shareholders |  |  |
Capital |  |  |
Number of shares held | 401,114,345 | 185,040,945 | 205,049,695
Shares Issued, Percentage | 23.30% | 10.80% | 11.90%
Common shares |  |  |
Capital |  |  |
Number of shares held | 573,627,483 | 573,627,483 | 573,627,483
Shares Issued, Percentage | 100.00% | 100.00% | 100.00%
Common shares | Metalurgica Gerdau S.A. |  |  |
Capital |  |  |
Number of shares held | 557,898,901 | 557,898,901 | 449,712,654
Shares Issued, Percentage | 97.30% | 97.30% | 78.40%
Common shares | Brazilian institutional investors |  |  |
Capital |  |  |
Number of shares held | 2,383,207 | 254,785 | 41,883,032
Shares Issued, Percentage | 0.40% | 0.00% | 7.30%
Common shares | Foreign institutional investors |  |  |
Capital |  |  |
Number of shares held | 4,836,488 | 7,254,556 | 11,122,498
Shares Issued, Percentage | 0.80% | 1.30% | 1.90%
Common shares | Other shareholders |  |  |
Capital |  |  |
Number of shares held | 6,811,349 | 6,521,703 | 69,211,761
Shares Issued, Percentage | 1.20% | 1.10% | 12.10%
Preferred shares |  |  |
Capital |  |  |
Number of shares held | 1,146,031,245 | 1,146,031,245 | 1,146,031,245
Shares Issued, Percentage | 100.00% | 100.00% | 100.00%
Preferred shares | Metalurgica Gerdau S.A. |  |  |
Capital |  |  |
Number of shares held | 95,469,922 | 95,471,131 | 202,806,626
Shares Issued, Percentage | 8.30% | 8.30% | 17.70%
Preferred shares | Brazilian institutional investors |  |  |
Capital |  |  |
Number of shares held | 224,073,547 | 155,227,424 | 92,721,295
Shares Issued, Percentage | 19.60% | 13.50% | 8.10%
Preferred shares | Foreign institutional investors |  |  |
Capital |  |  |
Number of shares held | 410,387,290 | 708,109,387 | 705,652,715
Shares Issued, Percentage | 35.80% | 61.80% | 61.50%
Preferred shares | Other shareholders |  |  |
Capital |  |  |
Number of shares held | 394,302,996 | 178,519,242 | 135,837,934
Shares Issued, Percentage | 34.40% | 15.60% | 11.90%
Treasury Stocks |  |  |
Capital |  |  |
Number of shares held | 23,495,028 | 10,401,599 | 10,710,213
Shares Issued, Percentage | 1.40% | 0.60% | 0.60%
Treasury Stocks | Common shares |  |  |
Capital |  |  |
Number of shares held | 1,697,538 | 1,697,538 | 1,697,538
Shares Issued, Percentage | 0.30% | 0.30% | 0.30%
Treasury Stocks | Preferred shares |  |  |
Capital |  |  |
Number of shares held | 21,797,490 | 8,704,061 | 9,012,675
Shares Issued, Percentage | 1.90% | 0.80% | 0.80%

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