C-spanner

C-spanner

n
(Tools) a sickle-shaped spanner having a projection at the end of the curve, used for turning large narrow nuts that have an indentation into which the projection on the spanner fits
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014