I used to make these out of lead core trolling line in many lengths from four inches to ten feet long. I whipped a loop on both ends. Today I have settled for a four foot model. By inserting these into a regular leader with a loop-to-loop connection, you can fish streamers and nymphs to extra depths. These do not work as well nor cast as well as the Scientific Anglers Sonar Sink Tip III Fly Lines but they are an inexpensive substitute.