Is there a chart or catalog, that I can get, that tells what size the different number sacks are. I mean a #12 is actually X" (or mm) in diameter and so on.

I have an assortment of sacks but don't know which one is what size so when I use up one particular size, don't know what I need to order to replace them.

I think, and please out there correct me if I am wrong, that the sack size number refers to the diameter of the opening in x/64" - so a #12 sack is 12/64" = 3/16".

There is a chart at the Pen Sac company, that tells what the official sizes for different makes and models of most major pens. The Pen Sac Company

However, take a look at the caveat from Richard Binder on this thread -Pen Sac Size Thread. A lot of the official sizes in the chart are too large.

J. Appleseed