| 摘要 |
PCT No. PCT/SE82/00327 Sec. 371 Date Jun. 9, 1983 Sec. 102(e) Date Jun. 9, 1983 PCT Filed Oct. 11, 1982 PCT Pub. No. WO83/01215 PCT Pub. Date Apr. 14, 1983.An extensible drill assembly comprising a plurality of separate drill members having different drill diameters which are arranged to permit assembly of two or more of the drill members into a continuous drill combination having a stepwise increasing diameter from the outermost drill member.
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