Here is the fly pattern sheet for the Improved F Fly. It is a fly designed by Marjan Fratnik, a Slovenian fishermen and fly tyer.
Daiichi 1100, 1110, or 1182, #12 – 22
8/0 brown, tan, yellow, olive dun, march brown or black
Superfine dubbing to match insect
Here is a link to my RiverKeeper Flies YouTube Channel: