
The thread has been cast on, and the hackle prepared and tied to the hook shank.

The thread is wrapped to the half way point on the shank. This space will accommodate the Thorax.

The silk abdomen thread is tied to the shank with the tying thread. The tying thread is left where it is. The silk is then wrapped toward the bend and back towards the eye, over the first layer, in touching wraps. This forms an abdomen of silk thread with no tying thread beneath.

The excess is trimmed off.

The dubbing brush to form the thorax is tied on, and the tying thread is wrapped down the shank towards the eye, leaving room to wrap the hackle.

The thorax is wrapped, excess trimmed. Now to complete the fly, the hackle can be wrapped, tied off, trimmed. The head can be formed and the fly is complete.
The result is a fly with a silk abdomen with only the shank beneath the silk. One could rib the abdomen using the silk abdomen thread instead of completely recovering the first layer that was put down when it was wrapped towards the bend. This would leave only one layer of base silk on the shank with an over rib of the same thread. The idea was that the layer of only silk would result in a more translucent abdomen.
Mark