They say 243 Imp 40°, I bought them thinking I was going to do a 243AI, and did a 6×284 instead. But that's what they sent me when I ordered them, they were listed as 243AI, several places have them listed with that part number as AI and several say Imp 40°, I don't honestly know, if there's a difference in this particular case, sorry I can't tell you specifically, but I've never used them.