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These shares were sold in multiple transactions in the open market at prices ranging from $15.00 to $15.12, inclusive. The reporting person undertakes to provide to NPK International Inc., any security holder of NPK International Inc., or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in footnote (2) to this Form 4."}],"balance_after":869326,"source":{"system":"sec-edgar","filing":"0000071829-26-000011","document":"wk-form4_1774556949.xml","document_sequence":1,"table":"nonDerivative","row_type":"transaction","position":1,"url":"https://www.sec.gov/Archives/edgar/data/71829/000007182926000011/wk-form4_1774556949.xml","form_type":"4"}},{"id":836271,"issuer":{"id":4885,"kind":"organization","name":"NPK International Inc.","symbol":"NPKI"},"owners":[{"id":42177,"kind":"person","name":"Fruge Mary Celeste","position":1,"cik":"0001975485","reported_name":"Fruge Mary Celeste","relationship":{"director":false,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"VP, General Counsel"}}],"security":"Non-Qualified Stock Option (right to buy)","published_at":"2026-03-18T20:35:48.000Z","date":"2026-03-16","kind":"exercise","planned":true,"acquired":false,"shares":1000,"price":0,"value":0.0,"ownership":{"direct":true},"footnotes":[{"field":"shares","element":"transactionShares","label":"F1","text":"The reported exercise of 1,000 options and subsequent sale of the shares acquired upon exercise occurred automatically pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on December 5, 2025."}],"balance_after":0,"derivative":{"exercise_price":4.32,"exercise_date":"2019-06-01","expiration_date":"2026-05-19","underlying":"Common Stock","underlying_shares":1000},"source":{"system":"sec-edgar","filing":"0001975485-26-000007","document":"edgardoc.xml","document_sequence":1,"table":"derivative","row_type":"transaction","position":3,"url":"https://www.sec.gov/Archives/edgar/data/71829/000197548526000007/edgardoc.xml","form_type":"4"}},{"id":836270,"issuer":{"id":4885,"kind":"organization","name":"NPK International Inc.","symbol":"NPKI"},"owners":[{"id":42177,"kind":"person","name":"Fruge Mary Celeste","position":1,"cik":"0001975485","reported_name":"Fruge Mary Celeste","relationship":{"director":false,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"VP, General Counsel"}}],"security":"Common Stock","published_at":"2026-03-18T20:35:48.000Z","date":"2026-03-16","kind":"sale","planned":true,"acquired":false,"shares":1000,"price":13.56,"value":13560.0,"ownership":{"direct":true},"footnotes":[{"field":"shares","element":"transactionShares","label":"F1","text":"The reported exercise of 1,000 options and subsequent sale of the shares acquired upon exercise occurred automatically pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on December 5, 2025."},{"field":"price","element":"transactionPricePerShare","label":"F2","text":"These options were sold on the open market at price stated. The reporting person undertakes to provide to NPK International Inc., any security holder of NPK International Inc., or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of options sold."}],"balance_after":265213,"source":{"system":"sec-edgar","filing":"0001975485-26-000007","document":"edgardoc.xml","document_sequence":1,"table":"nonDerivative","row_type":"transaction","position":2,"url":"https://www.sec.gov/Archives/edgar/data/71829/000197548526000007/edgardoc.xml","form_type":"4"}},{"id":836269,"issuer":{"id":4885,"kind":"organization","name":"NPK International Inc.","symbol":"NPKI"},"owners":[{"id":42177,"kind":"person","name":"Fruge Mary Celeste","position":1,"cik":"0001975485","reported_name":"Fruge Mary Celeste","relationship":{"director":false,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"VP, General Counsel"}}],"security":"Common Stock","published_at":"2026-03-18T20:35:48.000Z","date":"2026-03-16","kind":"exercise","planned":true,"acquired":true,"shares":1000,"price":4.32,"value":4320.0,"ownership":{"direct":true},"footnotes":[{"field":"shares","element":"transactionShares","label":"F1","text":"The reported exercise of 1,000 options and subsequent sale of the shares acquired upon exercise occurred automatically pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on December 5, 2025."}],"balance_after":266213,"source":{"system":"sec-edgar","filing":"0001975485-26-000007","document":"edgardoc.xml","document_sequence":1,"table":"nonDerivative","row_type":"transaction","position":1,"url":"https://www.sec.gov/Archives/edgar/data/71829/000197548526000007/edgardoc.xml","form_type":"4"}},{"id":852697,"issuer":{"id":4885,"kind":"organization","name":"NPK International Inc.","symbol":"NPKI"},"owners":[{"id":42177,"kind":"person","name":"Fruge Mary Celeste","position":1,"cik":"0001975485","reported_name":"Fruge Mary Celeste","relationship":{"director":false,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"VP, General Counsel"}}],"security":"Non-Qualified Stock Option (right to buy)","published_at":"2026-03-10T20:29:24.000Z","date":"2026-03-06","kind":"exercise","planned":true,"acquired":false,"shares":11193,"price":0,"value":0.0,"ownership":{"direct":true},"footnotes":[{"field":"shares","element":"transactionShares","label":"F1","text":"The reported exercise of 11,193 options and subsequent sale of the shares acquired upon exercise occurred automatically pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on December 5, 2025."}],"balance_after":1000,"derivative":{"exercise_price":4.32,"exercise_date":"2019-06-01","expiration_date":"2026-05-19","underlying":"Common Stock","underlying_shares":11193},"source":{"system":"sec-edgar","filing":"0001975485-26-000005","document":"edgardoc.xml","document_sequence":1,"table":"derivative","row_type":"transaction","position":3,"url":"https://www.sec.gov/Archives/edgar/data/71829/000197548526000005/edgardoc.xml","form_type":"4"}},{"id":852696,"issuer":{"id":4885,"kind":"organization","name":"NPK International Inc.","symbol":"NPKI"},"owners":[{"id":42177,"kind":"person","name":"Fruge Mary Celeste","position":1,"cik":"0001975485","reported_name":"Fruge Mary Celeste","relationship":{"director":false,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"VP, General Counsel"}}],"security":"Common Stock","published_at":"2026-03-10T20:29:24.000Z","date":"2026-03-06","kind":"sale","planned":true,"acquired":false,"shares":11193,"price":13.339,"value":149303.427,"ownership":{"direct":true},"footnotes":[{"field":"shares","element":"transactionShares","label":"F1","text":"The reported exercise of 11,193 options and subsequent sale of the shares acquired upon exercise occurred automatically pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on December 5, 2025."},{"field":"price","element":"transactionPricePerShare","label":"F2","text":"The price reported is the weighted average price. These options were sold in multiple transactions in the open market at prices ranging from $13.24 to $13.48, inclusive. The reporting person undertakes to provide to NPK International Inc., any security holder of NPK International Inc., or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of options sold at each separate price within the range set forth in footnote (2) to this Form 4."}],"balance_after":265213,"source":{"system":"sec-edgar","filing":"0001975485-26-000005","document":"edgardoc.xml","document_sequence":1,"table":"nonDerivative","row_type":"transaction","position":2,"url":"https://www.sec.gov/Archives/edgar/data/71829/000197548526000005/edgardoc.xml","form_type":"4"}},{"id":852695,"issuer":{"id":4885,"kind":"organization","name":"NPK International Inc.","symbol":"NPKI"},"owners":[{"id":42177,"kind":"person","name":"Fruge Mary Celeste","position":1,"cik":"0001975485","reported_name":"Fruge Mary Celeste","relationship":{"director":false,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"VP, General Counsel"}}],"security":"Common Stock","published_at":"2026-03-10T20:29:24.000Z","date":"2026-03-06","kind":"exercise","planned":true,"acquired":true,"shares":11193,"price":4.32,"value":48353.76,"ownership":{"direct":true},"footnotes":[{"field":"shares","element":"transactionShares","label":"F1","text":"The reported exercise of 11,193 options and subsequent sale of the shares acquired upon exercise occurred automatically pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on December 5, 2025."}],"balance_after":276406,"source":{"system":"sec-edgar","filing":"0001975485-26-000005","document":"edgardoc.xml","document_sequence":1,"table":"nonDerivative","row_type":"transaction","position":1,"url":"https://www.sec.gov/Archives/edgar/data/71829/000197548526000005/edgardoc.xml","form_type":"4"}},{"id":860193,"issuer":{"id":4885,"kind":"organization","name":"NPK International Inc.","symbol":"NPKI"},"owners":[{"id":42176,"kind":"person","name":"Piontek Gregg","position":1,"cik":"0001418328","reported_name":"Piontek Gregg","relationship":{"director":false,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"Senior Vice President and CFO"}}],"security":"Non-Qualified Stock Option (right to buy)","published_at":"2026-03-05T22:50:16.000Z","date":"2026-03-04","kind":"exercise","planned":true,"acquired":false,"shares":73590,"price":0,"value":0.0,"ownership":{"direct":true},"footnotes":[{"field":"shares","element":"transactionShares","label":"F1","text":"The reported exercise of 73,590 options and subsequent sale of the shares acquired upon exercise occurred automatically pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on December 3, 2025."}],"balance_after":0,"derivative":{"exercise_price":4.32,"exercise_date":"2019-06-01","expiration_date":"2026-05-19","underlying":"Common Stock","underlying_shares":73590},"source":{"system":"sec-edgar","filing":"0001418328-26-000002","document":"edgardoc.xml","document_sequence":1,"table":"derivative","row_type":"transaction","position":5,"url":"https://www.sec.gov/Archives/edgar/data/71829/000141832826000002/edgardoc.xml","form_type":"4"}},{"id":860192,"issuer":{"id":4885,"kind":"organization","name":"NPK International Inc.","symbol":"NPKI"},"owners":[{"id":42176,"kind":"person","name":"Piontek Gregg","position":1,"cik":"0001418328","reported_name":"Piontek Gregg","relationship":{"director":false,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"Senior Vice President and CFO"}}],"security":"Common Stock","published_at":"2026-03-05T22:50:16.000Z","date":"2026-03-04","kind":"sale","planned":true,"acquired":false,"shares":35000,"price":14.0169,"value":490591.5,"ownership":{"direct":true},"footnotes":[{"field":"shares","element":"transactionShares","label":"F3","text":"The reported sale of 35,000 shares occurred automatically pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on December 3, 2025."},{"field":"price","element":"transactionPricePerShare","label":"F4","text":"The price reported is the weighted average price. These shares were sold in multiple transactions in the open market at prices ranging from $13.68 to $14.31, inclusive. The reporting person undertakes to provide to NPK International Inc., any security holder of NPK International Inc., or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in footnote (2) to this Form 4."}],"balance_after":884326,"source":{"system":"sec-edgar","filing":"0001418328-26-000002","document":"edgardoc.xml","document_sequence":1,"table":"nonDerivative","row_type":"transaction","position":3,"url":"https://www.sec.gov/Archives/edgar/data/71829/000141832826000002/edgardoc.xml","form_type":"4"}},{"id":860191,"issuer":{"id":4885,"kind":"organization","name":"NPK International Inc.","symbol":"NPKI"},"owners":[{"id":42176,"kind":"person","name":"Piontek Gregg","position":1,"cik":"0001418328","reported_name":"Piontek Gregg","relationship":{"director":false,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"Senior Vice President and CFO"}}],"security":"Common Stock","published_at":"2026-03-05T22:50:16.000Z","date":"2026-03-04","kind":"sale","planned":true,"acquired":false,"shares":73590,"price":14.0979,"value":1037464.461,"ownership":{"direct":true},"footnotes":[{"field":"shares","element":"transactionShares","label":"F1","text":"The reported exercise of 73,590 options and subsequent sale of the shares acquired upon exercise occurred automatically pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on December 3, 2025."},{"field":"price","element":"transactionPricePerShare","label":"F2","text":"The price reported is the weighted average price. These options were sold in multiple transactions in the open market at prices ranging from $14.00 to $14.31, inclusive. The reporting person undertakes to provide to NPK International Inc., any security holder of NPK International Inc., or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of options sold at each separate price within the range set forth in footnote (2) to this Form 4."}],"balance_after":919326,"source":{"system":"sec-edgar","filing":"0001418328-26-000002","document":"edgardoc.xml","document_sequence":1,"table":"nonDerivative","row_type":"transaction","position":2,"url":"https://www.sec.gov/Archives/edgar/data/71829/000141832826000002/edgardoc.xml","form_type":"4"}},{"id":860190,"issuer":{"id":4885,"kind":"organization","name":"NPK International Inc.","symbol":"NPKI"},"owners":[{"id":42176,"kind":"person","name":"Piontek Gregg","position":1,"cik":"0001418328","reported_name":"Piontek Gregg","relationship":{"director":false,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"Senior Vice President and CFO"}}],"security":"Common Stock","published_at":"2026-03-05T22:50:16.000Z","date":"2026-03-04","kind":"exercise","planned":true,"acquired":true,"shares":73590,"price":4.32,"value":317908.8,"ownership":{"direct":true},"footnotes":[{"field":"shares","element":"transactionShares","label":"F1","text":"The reported exercise of 73,590 options and subsequent sale of the shares acquired upon exercise occurred automatically pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on December 3, 2025."}],"balance_after":992916,"source":{"system":"sec-edgar","filing":"0001418328-26-000002","document":"edgardoc.xml","document_sequence":1,"table":"nonDerivative","row_type":"transaction","position":1,"url":"https://www.sec.gov/Archives/edgar/data/71829/000141832826000002/edgardoc.xml","form_type":"4"}},{"id":883557,"issuer":{"id":4885,"kind":"organization","name":"NPK International Inc.","symbol":"NPKI"},"owners":[{"id":21945,"kind":"person","name":"Lewis Michael A","position":1,"cik":"0001423238","reported_name":"Lewis Michael A","relationship":{"director":true,"officer":false,"ten_percent_owner":false,"other":false}}],"security":"Common Stock","published_at":"2026-02-25T22:00:55.000Z","date":"2026-02-23","kind":"sale","planned":true,"acquired":false,"shares":2013,"price":14.3052,"value":28796.3676,"ownership":{"direct":true},"footnotes":[{"field":"shares","element":"transactionShares","label":"F1","text":"The reported sale of 2,013 shares occurred automatically pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on March 7, 2025."},{"field":"price","element":"transactionPricePerShare","label":"F2","text":"The price reported is the weighted average price. These shares were sold in multiple transactions in the open market at prices ranging from $14.11 to $14.43, inclusive. The reporting person undertakes to provide to NPK International Inc., any security holder of NPK International Inc., or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in footnote (2) to this Form 4."}],"balance_after":131333,"source":{"system":"sec-edgar","filing":"0001423238-26-000002","document":"edgardoc.xml","document_sequence":1,"table":"nonDerivative","row_type":"transaction","position":1,"url":"https://www.sec.gov/Archives/edgar/data/71829/000142323826000002/edgardoc.xml","form_type":"4"}},{"id":934813,"issuer":{"id":4885,"kind":"organization","name":"NPK International Inc.","symbol":"NPKI"},"owners":[{"id":42177,"kind":"person","name":"Fruge Mary Celeste","position":1,"cik":"0001975485","reported_name":"Fruge Mary Celeste","relationship":{"director":false,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"VP, General Counsel"}}],"security":"Restricted Stock Units","published_at":"2026-01-21T21:40:59.000Z","date":"2025-06-01","kind":"exercise","planned":false,"acquired":false,"shares":17274,"price":0,"value":0.0,"ownership":{"direct":true},"footnotes":[{"field":"shares","element":"transactionShares","label":"F1","text":"On June 3, 2025, the filed Form 4 inadvertently reported the conversion of vested restricted stock units into 17,247 shares instead of 17,274 shares, which was a scrivener's error."},{"field":"derivative.exercise_date","element":"exerciseDate","label":"F2","text":"Grant of restricted stock units that vest in one-third increments on June 1 of each subsequent year after grant and settle in shares."},{"field":"derivative.expiration_date","element":"expirationDate","label":"F2","text":"Grant of restricted stock units that vest in one-third increments on June 1 of each subsequent year after grant and settle in shares."},{"field":"derivative.underlying_shares","element":"underlyingSecurityShares","label":"F1","text":"On June 3, 2025, the filed Form 4 inadvertently reported the conversion of vested restricted stock units into 17,247 shares instead of 17,274 shares, which was a scrivener's error."}],"balance_after":17274,"derivative":{"exercise_price":0,"underlying":"Common Stock","underlying_shares":17274},"source":{"system":"sec-edgar","filing":"0001975485-26-000003","document":"edgardoc.xml","document_sequence":1,"table":"derivative","row_type":"transaction","position":2,"url":"https://www.sec.gov/Archives/edgar/data/71829/000197548526000003/edgardoc.xml","form_type":"4/A","original_submission_date":"2025-06-03"}},{"id":934812,"issuer":{"id":4885,"kind":"organization","name":"NPK International Inc.","symbol":"NPKI"},"owners":[{"id":42177,"kind":"person","name":"Fruge Mary Celeste","position":1,"cik":"0001975485","reported_name":"Fruge Mary Celeste","relationship":{"director":false,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"VP, General Counsel"}}],"security":"Common Stock","published_at":"2026-01-21T21:40:59.000Z","date":"2025-06-01","kind":"exercise","planned":false,"acquired":true,"shares":17274,"price":0,"value":0.0,"ownership":{"direct":true},"footnotes":[{"field":"shares","element":"transactionShares","label":"F1","text":"On June 3, 2025, the filed Form 4 inadvertently reported the conversion of vested restricted stock units into 17,247 shares instead of 17,274 shares, which was a scrivener's error."}],"balance_after":265213,"source":{"system":"sec-edgar","filing":"0001975485-26-000003","document":"edgardoc.xml","document_sequence":1,"table":"nonDerivative","row_type":"transaction","position":1,"url":"https://www.sec.gov/Archives/edgar/data/71829/000197548526000003/edgardoc.xml","form_type":"4/A","original_submission_date":"2025-06-03"}},{"id":989460,"issuer":{"id":4885,"kind":"organization","name":"NPK International Inc.","symbol":"NPKI"},"owners":[{"id":21945,"kind":"person","name":"Lewis Michael A","position":1,"cik":"0001423238","reported_name":"Lewis Michael A","relationship":{"director":true,"officer":false,"ten_percent_owner":false,"other":false}}],"security":"Common Stock","published_at":"2025-11-25T22:25:26.000Z","date":"2025-11-24","kind":"sale","planned":true,"acquired":false,"shares":2013,"price":12.0001,"value":24156.2013,"ownership":{"direct":true},"footnotes":[{"field":"shares","element":"transactionShares","label":"F1","text":"The reported sale of 2,013 shares occurred automatically pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on March 7, 2025."},{"field":"price","element":"transactionPricePerShare","label":"F2","text":"The price reported is the weighted average price. These shares were sold in multiple transactions in the open market at prices ranging from $11.65 to $12.13, inclusive. The reporting person undertakes to provide to NPK International Inc., any security holder of NPK International Inc., or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in footnote (2) to this Form 4."}],"balance_after":133346,"source":{"system":"sec-edgar","filing":"0001423238-25-000004","document":"edgardoc.xml","document_sequence":1,"table":"nonDerivative","row_type":"transaction","position":1,"url":"https://www.sec.gov/Archives/edgar/data/71829/000142323825000004/edgardoc.xml","form_type":"4"}},{"id":1023818,"issuer":{"id":4885,"kind":"organization","name":"NPK International Inc.","symbol":"NPKI"},"owners":[{"id":41168,"kind":"person","name":"LANIGAN MATTHEW","position":1,"cik":"0001672978","reported_name":"LANIGAN MATTHEW","relationship":{"director":true,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"President & CEO"}}],"security":"Common Stock","published_at":"2025-10-07T00:19:43.000Z","date":"2025-10-03","kind":"gift","planned":false,"acquired":false,"shares":770249,"price":0,"value":0.0,"ownership":{"direct":true},"footnotes":[{"field":"balance_after","element":"sharesOwnedFollowingTransaction","label":"F1","text":"The reported transfer of 770,249 shares reflects a gift of these shares from the reporting person to his living trust, of which the reporting person and his spouse are trustees."}],"balance_after":325664,"source":{"system":"sec-edgar","filing":"0001672978-25-000004","document":"edgardoc.xml","document_sequence":1,"table":"nonDerivative","row_type":"transaction","position":1,"url":"https://www.sec.gov/Archives/edgar/data/71829/000167297825000004/edgardoc.xml","form_type":"4"}},{"id":1026160,"issuer":{"id":4885,"kind":"organization","name":"NPK International Inc.","symbol":"NPKI"},"owners":[{"id":40317,"kind":"person","name":"Briggs Lori","position":1,"cik":"0001880836","reported_name":"Briggs Lori","relationship":{"director":false,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"VP & President, Ind. 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