a threaded fastener, used with a nut for connecting metal parts, having a thread diameter of about 1/4 inch (6.4 mm) or more and a square or hexagonal head for tightening by a wrench.
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British Dictionary definitions for machine bolt
a fastening bolt with a machine-cut thread
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012