When inserted into a conduit run, it provides a means to attach wires or fish line at one end and pull them out through the other. The flat, spring metal design makes it extremely flexible and capable of navigation through elbows and turns. It is typically sold in 1/8, 3/16 and 1/4" widths with lengths from 25 to 100'. For convenience, they are also sold within fish dispenser reels to automatically extend and retract the fish tape but most people buy the inexpensive wire fish only and store it in a short piece of Greenfield.