These ones are tied on 1/0 Gami B10s hooks with Wapsi "Perfect Popper" heads size 4.
I'm still trying to find the best head/hook combo. I had a couple packs of the absolute perfect size heads a handful of years ago that allowed me to tie on 2/0 Ahrex Predator Stinger hooks and they would ride absolutely perfectly. Unfortunately I didn't take note of the specifics of those heads and when I ran out I haven't been able to find them. Now it seems every head I find is either way too large for what I'm going for, or just slightly too small. When too small they have a hard time keeping the fly tied on a heavier hook riding right on the surface...they have a tendency to pull under after a few strips.
So I'm experimenting with these slightly smaller heads and using them on slightly smaller hooks. The gap seems fine on these hooks with the head on, and I've caught albacore on them in the past so I know they're strong enough. Just wish I hadn't been dumb and actually saved the details of those original heads as they were just perfect.