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Well drilling tool - with central pilot bit and upper overlapping follower bits
Well drilling tool - with central pilot bit and upper overlapping follower bits
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机译:钻井工具-具有中央导向钻头和上部重叠从动钻头
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摘要
A well drilling tool has a central pilot bit rigid with the drill string and a set of additional bits mounted on freely rotatable shafts parallel to the drill string so that each additional bit lies above the pilot bit and in overlapping relation thereto.
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