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公开(公告)号：US1856512A
公开(公告)日：1932-05-03
申请号：US33203529
申请日：1929-01-12
Applicant: ROBERT D PEARSON
Inventor： SCHOFIELD JOHN C , JOHNSON VERNER A
IPC: E21B33/06
CPC classification number: E21B33/061
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