It is best imitated on a size 18 or even a 20 hook depending on how the hook makers interpret their sizes.
Here is one way of making an attempt at a fake of the Iron Blue Dun (IBD) that was hinted at in the previous post. It differs from the traditional anatomy of herl bodied, hackled, dry flies in that it uses the spare end of tying thread as the rib. Again it is quick and easy to tie.
Tie in two herls from a primary wing feather of a Canada goose.
Make sure you have a few with you whenever you visit a water where they may live.