fish tape
A fish tape (also known as a draw wire or draw tape) is a tool used by electricians to route new wiring through walls.
Made of a narrow band of spring steel, by careful manipulation, the tape can be "fished" (guided) through the confined spaces within wall cavities. Once guided through, the new wiring can be pulled into the wall by attaching it to the end of the fish tape and pulling the tape back from whence it came.
Design
Fish tapes are usually stored coiled on a plastic reel. Because of this, they have a natural curvature and it is this curvature that allows them to be guided. By manipulating the reel, the end of the tape can be directed slightly. The tape is rigid enough that it can then be pushed in the direction in which it is pointing. In this way it can be easily guided through an empty wall cavity. Thermal insulation, firestops, pipes, HVAC ducts, electrical conduits, and other obstructions make use of a fish tape more challenging.
Double use
Occasionally, two fish tapes are used from opposite ends of the wall. Because they each have a hooked end, one fish tape is capable of catching the other, and the one tape can then be pulled back, carrying the second tape out with it. Electricians have been known to go so far as hooking up a battery and a doorbell or buzzer to their two fish tapes so that when the ends of the two tapes make contact within the wall, the bell rings.
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
