I'm thinking a 4/0 hook should be the one to pair with the 4G4... my understanding is that the last digit (on any of the Herter's jig molds) was related to size in eighths of an ounce, so a 4G1 would be 1/8oz, a 4G2 would be 1/4oz and so on. And the rule of thumb would be to use a corresponding step in hook size with each, so 1/0 hook with 1/8oz, 2/0 hook with 1/4oz, and so on.
A quick internet search will turn up lots of pictures with various series molds side by side, confirming the relative size differences, but I only found one source (worthpoint) referencing the hook correlation.
Interesting information! That's the first time I had heard that, but makes sense if true. I've never been one to always agree with what is recommended on a mold for hook sizes, and most of the time for my own use, eye balled the sizes. So, if it fit and did what I needed, that's what I used. I didn't get the chance to check my molds today either. Had to go into town to ship a package to S. Korea and frankly forgot. International shipping is always fun to deal with.
