| 摘要 |
A target includes a rim, a ring engaged in the rim, a number of depressions formed in the rear portion of the ring, a frame having a number of spaces and a number of fins formed in the outer peripheral portion, a protrusion formed on each of the fins for engagement with the depressions of the ring. The protrusions of the fins are disengaged from the depressions and engaged with the other depressions when the frame is rotated relative to the ring.
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