Howard, I missed the key word "undersized" the first time around too. Some make grips, even though they are a 58, still finished undersized on a 58 shaft. So with the 58 undersized grip on a 58 shaft, you still end up at a .855, .870, etc finished size. When you throw them on a .600 shaft, they still don't even get to a standard .900. More @Wikipedia
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