This article relies largely or entirely on a single source. (June 2018)
Made of a narrow band of spring steel, by careful manipulation, the tape can be guided through confined spaces such as wall cavities or conduits in many countries. The goal is to push toward an area where guide string has been dropped inside the confined space and to pull it through, so the guide string can then be used to pull through various types of wiring, such as phone wire, network cables or speaker wire. Fish tape is designed to pull through guide string only. Using it to directly pull the target wire can damage or warp the fish tape.
Inventor and Patent
Keith Leroy Wilson of Colorado Springs, CO, owner of the Electrical Construction Co, founded in 1947; invented the Fish Tape Snagger in order to save from 30 minutes up to several hours a day. Mr. Wilson filed the original patent on 29Mar1960 and Patent # 3,035,817 was awarded on 22May1962. US Patent Office 
Mr. Wilson's nickname for his original invention was "the snagger" and had signed an agreement with Graybar Electrical Co. Inc. for distribution and only advertised in trade magazines and direct mail. His "snagger" was an inexpensive tool that came in four sizes for half inch to six inch conduits, is made of stainless steel cable and has from eight to ten loops depending on the specific use weighing little more than a feather. Mr. Wilson says "his "snagger" eliminates abuse to fish tapes caused by worming and bending; it is something the workmen can always have on hand and ready for instant use".
Mr. Wilson was an intricate member in the building of Colorado Springs. He was Superintendent of the electrical work of Penrose Hospital as well as the expansion and remodel of The Broadmoor Hotel among other projects during his 33 year career. 
Keith Leroy Wilson was born 28Dec1905 and unfortunately died 23Feb1963 less than a year after his patent was awarded. His homemaker wife of 36 years, Sarah Nevada Wilson, did not know or was not advised to renew her husbands patents leaving the path open for others.
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.
The "tape" can be made from many different materials including steel, fiberglass, and nylon. The tape usually has a special end ranging from a hook or loop to a specialized fastener device to allow the user to attach the tape to the guide string (or a very light cable) before pulling.
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 sometimes attach a battery and a doorbell or buzzer to two fish tapes so that when the ends of the tapes make contact with each other (within the wall), the bell rings.
- H. Brooke Stauffer; Paul A. Rosenberg (29 September 2009). Residential Wiring. Jones & Bartlett Publishers. pp. 82–. ISBN 978-0-7637-8732-5.
- https://pdfpiw.uspto.gov/.piw?Docid=03035817&homeurl=http%3A%2F%2Fpatft.uspto.gov%2Fnetacgi%2Fnph-Parser%3FSect1%3DPTO1%2526Sect2%3DHITOFF%2526d%3DPALL%2526p%3D1%2526u%3D%25252Fnetahtml%25252FPTO%25252Fsrchnum.htm%2526r%3D1%2526f%3DG%2526l%3D50%2526s1%3D3,035,817.PN.%2526OS%3DPN%2F3,035,817%2526RS%3DPN%2F3,035,817&PageNum=&Rtype=&SectionNum=&idkey=NONE&Input=View+first+page. Retrieved 14 April 2021. Missing or empty
- (Colorado Springs Gazette). May 1962. Cite journal requires
|journal=(help); Missing or empty