The tough aggressive and light weight shimano slx m670 2013 10 speed rapidfire shifters pair with vivid indexing and 2 way release function light to the touch but positive and crisp vivid indexing provides a constant amount of shift lever force across all 10 sprockets 2 way release allows shifting from various riding positions the upper lever still performs the same shift function but it can now swing in either direction allowing it to be released by the thumb or index finger for use wi