studs need to be 3" min. K20/25 front studs are all too short.
k20/25 rotors are designed to run hub-centric on the back of the k20/25 hubs; so stud hole size on the rotors is not a big issue. The 14 bolt drums have a much smaller center bore than the K20/25 rotors do, so the rotors CANNOT seat hub-centrically on the back of the 14 bolt hubs. SO the best hope is that they can be staked lug-centrically to the hubs. The problem is the stud holes in the rotors are about .630ish". The commonly recommended dually studs are only .620-.622 - they are sloppy in the rotor holes. This means the rotor may not center on the hub. Not to mention grinding the heads on 32 studs sucks. I finally sourced a stud for a ford application that come closest to meeting all the needs of the above. Dorman 610-301 is 9/16-18, 3-1/4" long with a .622 knurl, but necks up just before the head. The portion that necks up seats in the rotor MUCH better; not a press fit, but not sloppy like the regular dually recommendations like 610-189 and 610-194. Plus the 610-301 head size fits into the relief in the rotors and requires no grinding. $1.99 at autozone, $2.48 at Advance, and $3.49 at Napa. Pix later. HTH someone someday.