Full Speed Ahead e Bike Drive Unit Spiders Engineered to withstand the beating that E-bikes often deliver, this FSA alloy spider for e Bike is meant to optimize the balance between weight, stiffness, and durability. SPECIFICATIONSVariant Manufacturer Part #50t840031064394104/64 BCD840031001627BCD104 Bosch Gen 3840031042972110 BCD Fazua840031029645BCD104 Bosch Gen 4840031062567Bosch Gen 4 Boost Spider BCD104840031062574 | Fsa | Full Speed Ahead Ebike Drive Unit Spiders 110 Bcd Fazua1 | Aluminum