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United States Patent
3,504,741
Issue Date:
April 7, 1970
Current U.S. Class:
166/356
; 166/267; 166/357; 166/366
Current International Class:
E21B 43/017 (20060101); E21B 43/00 (20060101); E21B 43/36 (20060101); E21B 43/34 (20060101)
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