e*thirteen e*spec Race Ebike Carbon Crank Arm Set Self Extractor- 165mm Bosch CX Gen4 Carbon BLKe*thirteen e*spec Race Ebike Carbon Crank Arm Set with Self Extractor 165mm Bosch CX Gen4 Carbon Black. The e*thirteen e*spec Race Carbon Crank Arm Set is designed to work with Bosch Gen 4 eBike motors. These carbon crank arms offer a slim Q factor and smaller overall profile while keeping e*thirteens proven crank technology at the forefront. An 8mm self extractor bolt is built into both arms for easy removal World Cup DH rated layup and construction