The Hypo-Allergenic Prong Collar is designed with a center plate, assembly chain, 2 O-rings and symmetrically arranged prongs. The center plate guarantees an equal distribution of pressure along the collar. Two O-rings serve for leash attachment. The prongs are evenly arranged around the length of the collar. So, when your dog starts to pull, the tension affects your dog all around his/her neck. And it means fewer neck injuries. This collar is made of curogan, a nickel free copper-tin-alloy. This collar is resistant to rust, anti-allergenic and anti-stain. It is recommended for dogs with sensitive skin and dogs with light coats. Over time it will antique and darken (the original look can be easily restored with the use of a polishing paste). Extra links can be purchased.