| 摘要 |
A tool includes a hub for slidably receiving a shaft which includes one or more projections. A driving stem has a number of internal teeth for engaging with the projection of the shaft. A spring may bias the projection of the shaft to engage with the internal teeth of the driving stem for positioning the driving stem. The driving stem is allowed to rotate about the shaft when the projection of the shaft is disengaged from the internal teeth by depressing the shaft against the spring.
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