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| 0000080172-20-000004-index.html | 2020-03-31 16:10:26 | |
| 0000080172-20-000004.txt | 2020-03-31 16:10:26 | |
| npk-20191231x10ka.htm | 119856 | 2020-03-31 16:10:26 |
| npk-20191231xex23_1.htm | 5108 | 2020-03-31 16:10:26 |
| npk-20191231xex31_1.htm | 8139 | 2020-03-31 16:10:26 |
| npk-20191231xex31_2.htm | 8549 | 2020-03-31 16:10:26 |