Our Chrome-plated training collars won't tarnish or rust. Adjusts by adding or removing links to fit dog's neck. Each link adds 1 inch to collar size. Size is the inside measurement of the collar. Allow 1 to 2 inches more than dog's exact neck size. If your dog's neck size is different from collar size listed, you must purchase additional links to get the proper fit. The links come 3 to a package.