Linear motion guide unit

A linear motion guide unit comprising:

• a rail having a pair of first raceway grooves extending parallel to each other in a longitudinal direction;
• a slider attached to the rail in a relatively movable manner, the slider having a pair of second raceway grooves facing the pair of first raceway grooves, respectively;
• and
• a plurality of balls as rolling elements;
• the rail and the slider forming looped paths for the plurality of rolling elements to circulate therethrough,
• the looped paths including
• load-carrying races each composed of the first and second raceway grooves,
• first circulation passages formed in the slider and extending in parallel with the load-carrying races, and
• pairs of second circulation passages formed in the slider and connecting the load-carrying races with the first circulation passages,
• the slider including a coil spring arranged in the first circulation passage so as to extend in the longitudinal direction,
• the coil spring including
• a pair of first regions provided at both ends in the longitudinal direction and fitted in the first circulation passage, and
• a second region smaller in diameter than the pair of first regions and positioned between the pair of first regions with a gap from an inner wall surface of the first circulation passage.