(1) [countersinking]∶在孔的顶部周围作成漏斗形凹坑的钻进操作

(2) [spot-facing]∶在孔的顶部周围作成圆柱形凹坑以便安置螺钉头或垫圈, 或者使连接零件能齐平安装

зенкерование, core drilling, hole enlarging