| 摘要 |
A system for securing a drill bit against rotation in a drilling rig of the type having a rotary table with an opening which is smaller than the drill bit. A breaker plate is supported in a frame below the rotary table. The breaker plate includes an irregularly shaped opening for engaging the drill bit when the drill string is raised. A sub is connected between the bit and the drill string. The sub can be rotated by the rotary table when the bit is held by the breaker plate to attach or detach the bit.
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