A gearbox code identifies the transmission family or manufacturer-defined variant; an OE part number identifies a specified original-equipment part or complete assembly within a manufacturer's parts system. One family can contain different application variants, and a part number can be revised or superseded while the broad gearbox label stays the same.
For example, 'ZF 8HP' is far too broad to order a control assembly, while a full unit identification plus the actual OE/service number can narrow the match. A casting number is also not automatically the orderable part number: it may refer to a common housing used in several finished assemblies.
Provide both the complete gearbox label and the original part reference where available. Match an alleged replacement number against an approved catalogue or documented supersession rather than treating similar-looking numbers as interchangeable.