They’re martingale-style training collars with two loops and a limited closure that give gentle control and help prevent dogs from slipping out.
Adjust using the metal slide: open the collar, slip it over your dog’s head, then tighten until only a couple of fingers fit comfortably under the collar.
Use a tape measure or a string where the collar will sit, note the length, and choose a size that lets you slip a couple of fingers comfortably under the fitted collar.
These collars are designed for dogs and are listed as suitable for all life stages.