| 摘要 |
<p>A gap adjustment mechanism (90) that moves an upper housing (64) in a direction close to a worm (70) is disposed in a fitting portion (80) between the upper housing (64) and a lower housing (65). The gap adjustment mechanism (90) is disposed in the fitting portion (80) on the side of the worm (70) or in the fitting portion (80) on the other side of the worm (70).
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