EARTH DRILLING EQUIPMENT
United States Patent 3426857

Inventors:
Bland, John
Publication Date:
02/11/1969
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Assignee:
MCALPINE & SONS LTD SIR ROBERT
Primary Class:
173/151
Other Classes:
173/165
International Classes:
E21B7/02; E21C1/02; E21B3/04
US Patent References:
3301334Drill rig
3330164Pipe rotating device with gear shift arrangement




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