The Fish-Skull Articulated Fish Spine is made up of specially designed articulated shanks in four different sizes. The Articulated Fish-Spine shanks allow you to tie multi-segmented, jointed, swimming flies with ultra-real action. Flies of different lengths can be created by combining different hook sizes and lengths with different shank lengths. The Fish-Skull Articulated Fish Spine is made of stainless steel and can be used for fresh or saltwater fishing.