The stages power meter is mounted to fsas hollow forged energy alloy non drive crank arm the bb30 version has across the board compatibility with fsa and vision bb30 modes note the megaexo model will only fit megaexo crank systems 2014 and newer and will not fit the megaexo omega model the stages power fsa model will not fit any fsa cranks with a pinch bolt style interface nor will the bb30 version fit any bb386evo models