Made since at least the 1500s, a pastry jigger (aka pastry crimper, aka jagging wheel) is designed to put a decorative edge on pastries. The edge is usually “jiggedy” (or “jaggedy”, if you prefer), but can also be used to create square or circular marks.
The difference between a pastry jigger and a pastry wheel is that a pastry jigger’s primary function is to leave markings, while the primary function of a pastry wheel (with a plain, straight edge) is to cut.
That being said, most pastry jiggers made now are wheels with ridges in them, designed to put a decorative edge on pastry, while cutting it out at the same time, thus combining the functionality of the two devices. Thus, the term “pastry jigger” is often now confused / used interchangeably with “pastry wheel”.
But there have been in the past pastry jiggers made that weren’t designed to cut pastry, but rather just to mark it — to “jig” the edge — without cutting it.
Crimp the edges of a pastry by pinching it with your fingers; or use the tines of a fork.
By the 1500s, devices which combined the functionality of pastry jiggers with pastry wheels were appearing.
Some early American ones, often carved from wood or whalebone as a pastime, would have given the pastry cook a choice of two or three different tool ends to use, such as a wheel that marked squares, one that left a wavy edge, one that simply cut a plain edge, or one that was a fork tine.
Antique ones are now collectibles.