Patent classifications
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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4/00
Drives for drilling, used in the borehole
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E21B4/16
Plural down-hole drives, e.g. for combined percussion and rotary drilling; Drives for multi-bit drilling units
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