You'd really think I'd know the answer to this, but I don't. In the H&H catalog, guides are listed as (sizes) 10, 4,3,2 ...striper down ... in Goldenwich's catalog they're sized#2/0, #1/0, #1, #2 etc. How does one make comparisons? Are H&H in mm's? If so, how does that measure in #2/0, or #3/0, or #1? Maybe what I'm trying to say is, is the 4 from H&H the same as the #2/0?