To deter a hog from rooting today is as simple as raising it indoors on cement, which is exactly what most large-scale hog farmers do. These pigs will never have a chance to root in dirt, but they won't have to go through the painful processes of being ringed.
Snout rings, slitters and other devices - called 'hog jewelry' by some collectors today - were used as deterrents against the hog's natural inclination to root in the dirt. The idea was to make the hog's nose so sore it lost interest in rooting.
Many different kinds of ringers were made and are collectibles today; a few even remain in use. They came in many different sizes and shapes, but basically all worked in the same way. The earliest hog ringers were plier-like tools that pierced the hog's snout. The tool usually bent a sharp piece of metal through the hog's nose, locking it in place. Hugh W. Hill patented many such models. One popular one used a triangle-like ring.
The Blaire Hog Ringer, another widely employed tool, used two sizes of round rings, and the Champion Hog Ringer used a double 'u'-shaped ring that made two passes through the snout instead of one. One type of hog ringer used pieces of sheet metal that had been cut out with tin snips, and another used a common horseshoe nail for a ring.
On July 1, 1879, Ozia A. Essig of Canton, Ohio, was granted patent number 217,082 for a unique hog ringer. The patent states that it was 'an improved device for inserting metallic rings in the noses of hogs to prevent them from rooting and provides the farmer or stock raiser with an implement that will enable him to form rings from nails, and to attach them to the animals, and thus avoid the necessity of obtaining rings specially prepared for the purpose.'
Figure 1 in the patent drawing shows how a horseshoe nail was gripped while it is bent to form a hook. This hook, as shown in the second figure, was then applied to the nose of the hog with the tool. There was one major drawback that probably doomed this tool to failure: Hill, who invented the original hog ringer, sold pre-formed hog rings for about 5 cents per hundred in 1898 (15 million were sold in two years), while the horseshoe nails proper for the tool sold for 7 cents per pound.