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United States Patent
3,113,620
Issue Date:
December 10, 1963
Current U.S. Class:
166/257
; 166/247; 376/275; 166/259
Current CPC Class:
E21B 43/2635 (20130101)
Current International Class:
E21B 43/263 (20060101); E21B 43/25 (20060101)
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