twist grip

noun

a handlebar control in the form of a ratchet-controlled rotating grip, used on some bicycles and motorcycles as a gear-change control and on motorcycles as an accelerator

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