For most of my mayfly duns I tie a Barr's Vis-A-Dun. It's a great thorax type pattern and one of my favorite's. Whether in a BWO size #18 or this March Brown in size #12 it's highly effective.
I even tie my Adam's in this pattern!
Click on the photo to enlarge...
Materials List:
Hook: MFC 7000 #12
Thread: 6/0 Danville in olive/brown
Tail: Coq De Leon
Rib: brown floss
Abdomen: DK#13 tan dubbing
Wing: Brown Copper Needloft yarn or Zelon
Hackle: Brown/olive grizzly in open turns, 3 behind wing and 3 in front
Thorax: DK#13 tan dubbing
note: cut "v" in bottom of hackle