E
FIXED CONSTRUCTIONS
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E21
EARTH OR ROCK DRILLING; MINING
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E21B
EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
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E21B7/00
Special methods or apparatus for drilling
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E21B7/02
Drilling rigs characterised by means for land transport; with their own drive; , e.g. skid mounting or wheel mounting
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E21B7/022
Control of the drilling operation; Hydraulic or pneumatic means for activation or operation
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