Both the A1C and AC feature aluminum construction with clamp-style hubs that are available with or without a keyway.  However, each style offers its own advantages.
The A1C style hub features an integrated clamping hub that provides the capability to handle the coupling’s peak torque rating for any bore size offered without the need for a key.  This design also offers larger bore size capacities compared to the AC style hubs and typically has faster Delivery.
The AC style hub is dimensionally identical to the steel clamp-style hub, but it offers a lower weight and inertia advantage due to the use of the lighter weight aluminum material.  Like the steel clamp-style hub, this design has a separate shaft collar which results in a smaller bore size capacity compared to the A1C style hubs and may require a key to handle the coupling’s peak torque rating.  Contact the factory for further details.