What are the number designations for. I have a 125 A and there are a few with other numbers like K&D 128 and so on. Is it the barrel sizes?

The numbers are different styles, I have #123a which are one piece winders, a #126 is wood handle with interchangeable heads, another goes in vise # unknown

I have a 128 that goes in the vise. (I generally just hold it in my hand.)