Fire eye expander 42t sprocketfire eyes 42t expander sprocket is the ideal addition for those converting to a 1x10 drivetrain or if you find your 2x10 drivetrain still leaves you struggling on those extended climbs fully cnc machined from 7075 t6 aluminium this expander provides excellent durability at a low weight it also comes with a 16t steel sprocket which helps to smooth the transition through the cassette features materialcnc machined 7075 t6 aluminium compatible with2x10 or 1x1