'Off the top of my head. Flank feathers are tricky to work with...they want to twist..the stem wants to twist. That can be dealt with, and I use these good looking, long fibered feathers on some soft hackle streamers. CDC..It is the best on wild ducks compared to the CDC that comes off the domestic ducks that is sold. I use only one type of the CDC...there are about 4 structural types of CDC feathers around the preen gland..the big fern looking CDC I use. It can be pinched down, and used as winging, and as an underwing to get flotation and especially the gray color I want found on many of the aquatic insect wings...then maybe deer hair over it as on a stimulator type of downwing fly. But I use the metallic looking smaller green feathers on the rump as well on soft hackle flies. And the small gray feathers on the wing I use for wings on a dry fly dun pattern when I want a more natural look for a PMD pattern let's say fished on smoother water where a trout gets a closer inspection of your fly. They are tough, and can be set in easily. I just tied a bunch of them up, and have the next Summer urge already. Other fibers off a feather can be used as tailing fibers. Lots of uses. Match up the right flank feather, and tie a Kelly Gallup Zoo Cougar streamer, and it becomes an awesome streamer....BUT, the right flank feather has to be used, and set in right, or the streamer spins, and no good.