Big-n-Buoyant:Mine may have been 5/8"... thanks for correcting, so someone doesn't go out and buy the wrong diameter.....
I'm not sure it was a correction -- I brought my newly-purchased shears with me and tried out both before I had a chunk cut off. They both fit, it just seemed that the 5/8" held them better, without relying on the bend that's at the pivot point.