Hog rings are used all over, including on hog noses. The ring is a wire shaped like a C, and the pliers have a groove in the pinching end that squeezes the C closed, bending it into a tight "ring" as is used to seal the end of a bag or sausage.
Three types are common for getting into tight spots.
The cheap ones for making cages and annoying hogs, may not be the best choice for upholstery.
