I’ve experienced this sort of thing with my car. it’s a old 50s car that had a engine swap and a few mods before I got it. so one one hand everything is universal but on the other hand I don’t know what is stock. I only know what sizes are currently under the hood. which wouldn’t be a problem if the guys at AutoZone or O’Reilly’s knew what the different sizes ment. Before I finally figured out what car my engine came from. id just measure the part I need. come in and tell them the part I need, and they would just sit confused until they just asked me what car is this part going into. sometimes the part happens to be stock bel air size, but sometimes they weren’t and the guy would have to bring the used part to the back. until they found something the right size. Hell even when I ordered online id have to wonder if I’m going to be fighting the “guarantee to fit your car thing.” because I don’t know if stock will work. Here at least you can navigate if you managed to find a conversation calculator. My measurement standards don’t matter no matter what unit I use.