I'm not really sure what you mean about the size? I know what a drill index is but I have looked on the sights that sell ferruls and the sizes don't make sense to me. what does it mean 20/19 or 21/23 in sizes? Please help me I'm new at this and don't want to mess up. Also you say build up with thread. that is on the rod it's self to build it up and how much can I go on that? thanks Walter. I hope you don't think I'm stupid for the questions I'm asking I just want to be sure before I start anything.