I meant 24s with 10/0 thread and that was pushing my tying abilities for some micro midges I was trying to match. Come to think of it they never worked. I think the standard jaws on the traveller are too bulky to do a 28 but I think they sell midge jaws that would work for a 28. I have yet to read AKs book so my hand position is probably way wrong but I get the job done(depending who you ask).
The lowest I go for trout patterns is a 20 but I try and get away with 18s and bigger as I hate trying to thread tippet on those size 20s to the hook. That is an art in itself