I'm not usually one to make a post like this, but this is something that has bugged me for a long time. Cummins guys used to always call ARP studs 425s and 625s, and it has always been somewhat of a pet peeve of mine. I wouldn't bring it up, but I'm seeing it more in the Duramax world now too. Maybe someone who uses this terminology can explain why because I don't know where the 425 designator came from unless someone just thought it sounded good. It makes no sense to me, but if explained, maybe I can get over it.