The specialized s works carbon road crank arms is a top end crank arm set the hollow carbon arms offer superior stiffness and the best strength to weight ratio on the market they have an oversized alloy spindle with hirth coupling interface which is very stiff and compact specialized have designed these cranks to fit their specialized road frames with osbb and pf30 bottom bracket shells but theyre also compatible with frames with bb30 bottom brackets these s works carbon road crank arms are