| 摘要 |
Mounted on the floor of an oil well derrick substructure is a support that is rockable on an axis perpendicular to the centerline of a well being drilled beneath the substructure. One end of an arm is pivotally mounted on the support on an axis transverse to the first mentioned axis, while the opposite end of the arm carries a pair of shoes having laterally opening pipe-receiving seats facing away from the arm. The free end of the arm can be swung toward and away from the well centerline and the arm support can be rocked to swing the arm laterally.
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