E thirteen trstrs dual ring roller kitreplacement roller kit for all trs dual devices chain devices fit in various places around a mountain bikes transmission and help to eliminate chain suck and chain slap when riding over rough terrain or landing from big drops there are a number of fitments some frames have iscg mounts which are lugs on the drive side of the bottom bracket shell and allow direct fitment to the frame other chain devices fit in between the bottom bracket and frame and requ