| 摘要 |
A ball screw is provided which makes it easy to determine the degree of deterioration of lubricating grease so that new lubricating grease can be supplied efficiently without loss. The ball screw includes a threaded shaft formed with a thread groove in its outer peripheral surface, a nut formed with a thread groove in its inner peripheral surface, and a plurality of balls rollably retained in a circulating passage comprising a helical passage formed between these thread grooves when the nut is fitted on the threaded shaft, and a passage connecting both ends of the helical passage. The balls and the circulating passage are lubricated by a lubricating grease which has a brightness of 1 or over and in which a base oil having a viscosity at 100° C. of 3.0-7.5 mm2/s is thickened by a urea-family thickener.
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