Lead-free sinks for river fishing, especially for salmon and sea trout. In Älvkarleby, for example, lead is banned and you use these to cast out and get your flies into the holes that exist. Use a three-way lure and attach first the main line, then a long leader to the fly, the line to the sinker should then be slightly thinner than the main line and leader so that it is the sinker you lose and not the fish if it gets stuck.