Funny you should ask this, as I just went through some hassle installing 3" ARP studs.
The rotors I have arent exactly stock, they're 5-lug, same dimensions as stock, though. The wheel studs I ordered for the rear axle pressed in nicely. The studs for the front, however, were slightly too large, and I cracked a rotor installing the first one. (I have a large press, and I was being careless, apparently) Anyway, the original 5-lug rotors I bought have a stud shoulder(not the actual knurled area, that's larger) diameter of .540"-.543", whereas the replacement 5-lug rotor I bought from the same place has a stud shoulder diameter of .549"-.550" The two rotors are obviously from different manufacturers.
You will be best off removing one of the studs from your rotor and measuring it. It will most likely be between .540"-.550". Make sure you measure the new studs before installing them, and they don't need to be that tight of a press fit. The knurl diameter changes slightly after installation because of crush, so I measured the shoulder part instead, as it remains constant. The summit or jegs tech guys can tell you the diameter of the shoulder area as well as the knurl area.
