Application Identifier 01 is used when identifying a device with a GTIN number: GTIN-13, GTIN-14 or GTIN-12.
AI (01) is used when it is a standard unit, e.g. a package or pallet containing the same thing every time the package or pallet is ordered. When identifying with GTIN-13 and GTIN-12, 0's are prefixed so that all 14 fields in the data format are filled in.
A 9-number preceded GTIN number indicates that the product is quantity variable and must appear with either AI 30, 3nnn or 8001.