A Suffix meaning on an ATV31.
Altivar 31 ATV31
Drive part number omits the A suffix.
The ATV***31A has the start/stop button, run button, and a potentiometer on the front of the drive. The ATV***31 without the "A" at the end of the part number does not have the start/stop, run, and potentiometer on the front of the drive.