模具零件采用紧固件法连接固定时,其螺钉拧入长度有一定要求,对于钢件一般要求螺钉拧入长度等于( )倍的螺钉直径或稍长。
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
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