What ever you choose, I recommend running the lower mounting bolts from the inside of the frame to the outside and snugging the button heads up to the frame, then put the rack on the threaded stud sticking outside of the frame and using a nylock nut to secure. This way there is no way you can strip the threads out of your frame (which is not uncommon on really bouncy rides with heavy weight). This is also the most secure you can make it, I promise! Be sure to use a button head on the rear drive side especially to be sure you have enough chain clearance for shifting into smallest cog.