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United States Patent
3,384,169
Issue Date:
May 21, 1968
Current U.S. Class:
166/357
; 166/267; 175/206
Current International Class:
E21B 43/01 (20060101); E21B 43/36 (20060101); E21B 43/34 (20060101); E21B 43/00 (20060101)
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