Our product catalog is organized numerically with a 3 or 4 digit prefix number. Each 3 or 4 digit prefix number tells you what the part is i.e. part number 0571025. 057 is a Zinc Metric Hex Head Bolt. The rest of the number, 1025 tells you the size, 10mm x 25mm. This is true in several instances but not all. Body clips are designated with a 500 or 501 prefix with Auveco's part number as the rest of the number in a lot of instances. Auveco is a widely recognized parts catalog in body shops so we used their numbers for simplicity of ordering.