The ABB 3BBR50000038983 is an ACH580-01-04A1-4 drive in Frame Size R1. That R1 frame tells you the physical footprint — how wide on the rail and how the gland plate lines up. It's the smallest frame in the ACH580 family, so it fits in tight panel real estate without cramming.
Frame Size R1 keeps the wiring channels clean and the derating curve predictable in a packed enclosure.