A jig's primary purpose is to provide repeatability, accuracy, and interchangeability in the manufacturing of products. A jig is often confused with a fixture; a fixture holds the work in a fixed location. A device that does both functions is called a jig.
An example of a jig is when a key is duplicated; the original is used as a jig so the new key can have the same path as the old one. Since the advent of automation and computer numerical controlled machines, jigs are often not required because the tool path is digitally programmed and stored in memory. Jigs may be made for reforming plastics. Jigs or templates have been known long before the industrial age. There are many types of jigs, and each one is custom-tailored to do a specific job.