U bolt n (Building) a metal bar bent into the shape of a U and threaded at both ends to receive securing nuts: used to secure leaf springs, ring bolts, shackles, etc Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014