What you're actually buying
The ABB ACH580-01-12A6-4+B056 is a frame 01 wall-mount drive from the ACH580-01 series, ordered with the +B056 option code appended to the base 12A6-4 current class — the same body the ACH580 HVAC/water family ships in, configured for a specific option package rather than a different rating.
Reading the order string
ACH580-01 is the family and frame: ACH580 is ABB's HVAC and water-oriented drive platform, the -01 suffix is the wall-mount form factor. The +B056 option suffix is layered on top of the base drive, which ships without it.
Same family, different current class
Stepping up the same ACH580-01 wall-mount family lands on the ACH580-01-014A-4 and the ACH580-01-023A-4 — both list 6.80 kgs per their weight rows, heavier than the 12A6-4 unit at 2.49 kgs. They stay in the same family line but are not drop-ins for the 12A6-4 BOM.