Unused hog rings kinda look like rounded staples. When you squeeze them with hog ringer pliers they form a ring capturing whatever happens to be in the center. They’re used in all sorts of applications, like fencing, landscaping, mattress and automobile seat construction, and even holding sausage casings closed.
For small jobs regular pliers may work, but if you have a lot of rings to form you’re gonna want a pair of hog ringer pliers like the pictured ones from Seymour. They cast the pliers from iron and zinc plate them. A thumb screw controls how far the jaws close, so you don’t crush the hog rings too much.
The pliers will run you anywhere from $8 to $10. A mess of hog rings will only run you a couple of bucks.