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苏联设计出几种供油井钻进用的小口径电钻。直径分别为170毫米和127毫米;前者用№8牙轮钻头钻进,后者用№6钻头钻进。
The Soviet Union has designed several small-diameter drills for oil well drilling. Diameter of 170 mm and 127 mm, respectively; the former with № 8 roller bit drilling, the latter with № 6 bit drilling.