The GA7FF uses a specific XPA belt profile. The manual gives the length (e.g., XPA 1032). Do not buy a generic auto parts store belt. The manual specifies the Atlas Copco part number because their belts are anti-static and oil-resistant. A standard belt will crack in 100 hours.
The parts manual categorizes components into several key systems. When ordering, you will need the specific part numbers found in the Atlas Copco GA7 parts list . atlas copco ga7ff parts manual