I really don't know, the machine shop picked them out. I got the guide plates from Edelbrock If I remember right. We used 7/16th studs for the rockers, the machinist thought it was a good idea. It's a mild roller cam but the open spring pressure is 320#s. I hope that helps. I used the regular rockers, not the self centering. The self centering looked too close to the retainers. These are the stainless rockers, not aluminum. I think they are fairly cheap. I would use them on a street motor but not on a race motor. I have a few aluminum ones I used for mock up and these are heavier and use needle bearings. I don't rev over 5500, the cam is out of breath above that.