Slide a 2.4mm tungsten bead onto a size 12 2X-long nymph hook — that bead is heavy enough on its own, so no lead. Start the brown 70 denier thread and build a small dam behind the bead to discourage it from sliding back.
Tail: take six or seven pheasant tail fibers, rolling them between your fingers if they cling together, and bind them in about one hook gap long with a couple of wraps.
Catch in the small copper wire rib around the middle of the shank, then catch in the medium pearl tinsel at the same point on the side, walking it so that by the time it reaches the back it sits on top of the hook.
Take the thread up to the two-thirds point — that is where the body stops and the thorax starts. Give the pheasant tail fibers a light spin, grip them in spring-loaded hackle pliers, and wrap them forward to the thread, adding another twist every couple of wraps. Catch off with a couple of wraps.
Thorax: take three to six strands of peacock herl, spin them lightly between your fingers — enough to keep them from spreading, not a tight rope — and make four to six wraps to build a thorax noticeably thicker than the thin body, the way most mayfly nymphs sit. Catch off right behind the bead.
Lay the pearl tinsel over the top and hold it with two temporary wraps while you check it is sitting square on top of the hook.
Wrap the wire rib forward over the pheasant tail body only — about three turns — and take two wraps on top of each other at the back of the thorax. Release the temporary wraps, pull the flash back out of the way, then finish the wire up through the peacock herl to lock the herl in. Helicopter the wire off. Stopping the rib short keeps it from matting down the flashback.
Fold the flash forward over the thorax and lock it in with a few extra wraps, then snip it off.
Pull back a CDC feather to make a tie-in point, catch it in with two or three wraps plus a couple more to lock it, and snip the front piece off. Take two wraps of CDC as if it were a hackle, catch it in behind the bead and snip the stem.
Pull the fibers back and fill the gap between the hackle and the bead with several solid wraps, then whip finish right behind the bead.
Bunch the long CDC fibers in your fingers at the length you want and pinch and pull to break them off rather than cutting the feather tips.