Official part numbers for Volkswagen vehicles are nine-digit numbers usually separated, either by spaces or hyphens, into groups of three digits, according to Aircooled.net. The site states that the groups of digits, read left to right, indicate the type and model of vehicle, the main and sub group of the part, the part component number and, if applicable to the part, the modification number.
The first digit of a VW part number refers to the part type, while the second and third digits refer to the VW model, states Aircooled.net. The fourth digit indicates the part's main category, such as engine, electrical or transmission, and the fifth and sixth digits reveal the part's sub category. The remaining three digits are the part's component number.
Some VW parts may have three letters at the end; these letters indicate a modification code if, for example, the part comes in different colors or sizes. Part numbers that begin with a zero indicate engine or mechanical parts that are likely to fit many different models of VW vehicles, according to The Bus Depot.
Only original manufacturer parts follow this numbering system. Part numbers which appear to follow VW's part numbering code are often aftermarket parts manufactured with part codes based on the VW system. A database of both original VW and aftermarket parts is available on Aircooled.net.