e*thirteen Helix Race Alloy e*spec Crank Arm Set - BOSCH SX-Brose S Mag-TQ HPR50 21.5mm Offset 165mm with Self Extractor Silver. A high-performance weight-optimized alternative to carbon fiber for riders who prefer alloy cranks. These 24mm ISIS interface cranks are engineered for compatibility with Bosch Gen 4 Brose S Mag TQ HPR 50 Fazua Yamaha Maxon and Specialized Brose motor systems. They come in short lengths starting at 155mm for improved pedal clearance and are tested to E-Enduro standards.