?扇形齿轮
... 天窗 scuttle; trap-door; skylight ... 扇形齿轮 gear sector; gear segment; s ... 扇形齿轮 cam gear quadrant; elevating arc; gear sector; geared sector; notched segment; quadrant gear; rack circle; scalloped wheel; sector gear; sector wheel; segment gear; tooth sector; toothed quadrant; toothed sector; toothed segment ...