Fsa afterburner 386 megaexo 10sp crankset the afterburner compact 386 megaexo feature ultra lightweight al6061 t6 hollow forged crank arms mated to a chromoly steel spindle it comes complete with a steel megaexo bottom bracket and 100 percent cnc al7075 t6 chainrings fsa afterburner 386 megaexo 10sp crankset specification hollow forged alloy arms low speed extruded al7050 bb30 spindle al7075 100 cnc chainrings chromoly chainring bolts available for 10 speed atb systems bcd 86mm weight 810