位于重型井架或桅架式井架顶部的固定的滑轮组（称之为滑车轮槽轮），通过该滑轮组钻井钢丝绳进行穿绳。

The fixed set of pulleys (called sheaves) located at the top of the derrick or mast, over which the drilling line is threaded.

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灯塔的顶部安装了一些典型的装置如走廊、人字形轻便井架、旗杆、分段装配玻璃。

The top of the beacon is fitted with the typical attributes such as a gallery, a mast, a flagstaff, and segmented glazing.

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