They are usually referring to the 8th digit of the VIN number which indicates the vehicle's engine type. I have no idea why they don't supply this info when they ask for the engine VIN digit, I didn't learn this until I started working on cars professionally and they somehow expect consumers looking for a part to know this.How do you find out the correct filter model? I have a 2013 Mazda 3 2.0 liter engine, and I don't see how to find it in the owners manual. The Pep Boys book lists a few different models, depending on a "VIN" number, such as "VIN 7," or VIN G," etc. What do those numbers mean? It's not the full Vehicle Identification Number, so it must be something else. Thanks.