| 摘要 |
PROBLEM TO BE SOLVED: To prevent rise in the rotational torque of an adjustable nut, score or service life decrease of a screw mechanism between the adjustable nut and a movable lead bolt, and lowering of the withstand voltage of the adjustable nut when the nut receives a lateral force. SOLUTION: Needle bearings 21 and 22 are inserted between the inner peripheries of a screw-receiving section 12, erected around a hole 4a and the hole 4a and the adjustable nut 14 on the internal surface side of a movable-side end plate 4 which has the hole 4a at its central part.
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