This is the sram rival oct 5339 tooth double crankset inc gxp bottom bracket the sram rival open core technology oct crankset shows the way forward for any serious cyclist putting power to the road while saving weight at the same time open core technology means the crank arms are hollow forged out of al 6066 alloy for maximum strength and mount our powerglide 10 speed chainrings oct construction is stronger and lighter than standard solid core alloy cranks powerglide chainrings are comp