Here is the fly pattern sheet for Fran Better’s Dark Haystack.
Mustad 9671, #10 – 18
Hot orange 4/0 or 5/0
Dark brownish deer hair
Dark brown muskrat or beaver
Larger bunch of same color deer hair
This is the fly pattern as described by Mike Valla in his book entitled The Founding Flies.
I’ve used 140 denier Danville thread for the fly on a #12 Mustad 9671.