| 摘要 |
A face mask includes an arcuate transparent sheet which extends about a central axis, and which has an upper engaging edge portion extending therealong. The upper engaging edge portion has a central positioning hole formed in a middle thereof to define a reference line with the central axis, two elongated first grooves formed respectively at two side ends of the upper engaging edge portion to define a first chord therebetween perpendicular to the reference line, and two elongated second grooves respectively inboard to the first grooves. The second grooves define a second chord therebetween perpendicular to the reference line. Each of the first and second grooves extends along the upper engaging edge portion. Each second groove is longer than each first groove. As such, the face mask can be assembled on different kinds of helmets and the like.
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