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3379420
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Patent number 3,379,420
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Issue date Apr 23, 1968
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B28 - WORKING CEMENT, CLAY, OR STONE
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3218044
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Patent number 3,218,044
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Issue date Nov 16, 1965
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B28 - WORKING CEMENT, CLAY, OR STONE
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3124272
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Patent number 3,124,272
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Issue date Mar 10, 1964
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B28 - WORKING CEMENT, CLAY, OR STONE