Good question! The challenges of steelhead fishing on the Pacific Northwest rivers, like the need to deliver big flies in tough conditions with very little backcast clearance, using lighter and shorter rods to match the size of the quarry, and considering that control of the fly's speed and location in the water column is critical, resulted in the development of the Skagit lines and the Skagit, or Pacific Northwest (PNW), style of Spey casting. Specialized spey casts such as the Snap T and the Perry Poke were created to refine the use of the Skagit lines.
Skagit lines are built as a shooting head and have also recently been designed with an integrated shooting/running line. Like the Scandinavian head, the length of most Skagit heads is in the 2.5-3.5 times the rod length range, but the rods are typically shorter. Skagit heads are unlike many other fly lines in that they have very little taper and are pretty much one thick, level section of line. This helps to carry the weight of a heavy sink tip and large fly for long casts with little room for a backcast.
Originally, Skagit lines were used to throw sink tips of varying densities (T-8, T-11, T-14, T-17) but now many spey casters are using Skagit lines for fishing under any conditions, and are now using floating tips on Skagit heads. The floating tips are 15’ long and vary in grain weight to match the weight of your Skagit line. The important thing about using any tip for Skagit style lines is that they have enough grain weight to properly anchor your fly line. Poly leaders that work well on Scandi lines are generally too light and will cause the caster to pull their anchor and struggle with their casting. A good anchor is critical to allow you to form a D-loop and maintain load in the rod throughout the casting stroke.