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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17/00
Drilling rods or pipes; Flexible drill strings; Kellies; Drill collars; Sucker rods; Cables;; Casings; Tubings
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E21B17/10
Wear protectors; Centralising devices; , e.g. stabilisers
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E21B17/1014
Flexible or expansible centering means, e.g. with pistons pressing against the wall of the well
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E21B17/1021
with articulated arms or arcuate springs
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