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3897110
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Patent number 3,897,110
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Issue date Jul 29, 1975
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E21 - EARTH DRILLING MINING
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3578811
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Patent number 3,578,811
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Issue date May 18, 1971
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E21 - EARTH DRILLING MINING
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3482879
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Patent number 3,482,879
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Issue date Dec 9, 1969
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E21 - EARTH DRILLING MINING
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3291533
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Patent number 3,291,533
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Issue date Dec 13, 1966
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E21 - EARTH DRILLING MINING