It's all related to where the merch is sitting when you order. There is an online auto parts store called RockAuto that will let you know across the site which

It's all related to where the merch is sitting when you order. There is an online auto parts store called RockAuto that will let you know across the site which items are sitting in the same warehouse as other items in your cart. A lot of the stuff is standard auto parts so there will be like eight identical gas caps made by different vendors that are all priced within a few cents of each other. They all are located in different warehouses so I'll usually pick the parts I don't have as much choice over and then go back and pick the jellybean parts that happen to be in the same warehouse. They don't do free shipping so it really helps reduce shipping costs when you only have one box coming. It's also nice just getting all of your parts at once instead of having to wait for different ones to come in and not being able to work on anything until you get them all anyway. I'll play around with which identical parts I choose just to make sure I'm picking all the parts I need from the same, closest warehouse.