The shimano deore m615 double 3824 10 speed chainset is a 2 piece design chainset features an external bottom bracket system which is a lightweight rigid design that is incredibly strong and durable the sg x chainring with patented spike pins give smooth and fast gear shifts under load the outer chainring is made from a lightweight aluminium and a steel inner chainring the lightweight and rigid steel bottom bracket axle is designed to fit hollowtech ii bottom brackets the deore m615 chains