| 摘要 |
An apparatus on a drilling tower platform for gripping a vertically extending drill casing includes a drill bushing having a pair of casing gripping assemblies mounted thereon, one assembly of the pair including a first and second gripping jaw, with a common actuator therebetween, and the other assembly of the pair including a third and fourth gripping jaw, with a common actuator therebetween, the pair of gripping assemblies being positioned around the bushing so that the first and fourth gripping jaws grip the casing at approximately diametrically opposed locations and so that the second and third gripping jaws grip the casing at approximately diametrically opposed locations approximately 90 degrees from the first and fourth gripping jaws, as measured around the bushing.
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