Hi Scrollman,
Welcome to the forum.
I cannot recall off hand, but it is not only the weight but how the weight is distributed. For hams, I like to smoke them on their sides, so a lot more weight is going to be pushing down on one area more than another. So a 11 lb. ham is going to put more stress on a rack, than a brisket that can weigh more. So long story short, when I'm smoking ham, I double up the racks for peace of mind. I also do this for turkeys that are over 10 lbs., or if I'm smoking the turkey vertically.