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我队为了巩固小口径钻探工作，重点抓质量，根据本地区煤层特点，吸取了外单位取煤工具的优点，设计了外管直径为73毫米（壁厚3.75毫米），
In order to consolidate the work of small-diameter drilling, our team focused on the quality and learned the advantages of the coal extraction tools of the external units according to the characteristics of coal seams in this area. The outer diameter of the outer pipe was 73mm (wall thickness: 3.75mm)