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When a thumbtack cannot be pulled off from a message board,
an elastic iron sheet can be used to press the center of a thumbtack, and its edge will bounce.
One can easily pull a thumbtack off by the arc of its edge.
Quite a few people get injured when they step on fallen thumbtacks due to negligence.
The arc shape of nicks on the edge of a thumbtack can reduce the area of a thumbtack.
When it falls, it touches the ground with its three points, and its sharp pin will not face upward to hurt anyone
Asia university
Taichung, Taiwan
Asia university
Taichung, Taiwan
YUTI HUANG
SHUOTING CHUANG