How to size your dog for the fur saver: Please measure the width of your dog's neck and add 2 to 3 inches to determine an appropriate collar length. Curogan - is a copper-tin-alloy with a high copper portion and some additives which make the material strong - but without any nickel.Therefore these chains avoid a discolouration of fair haired dogs.After selling these articles for six years, the experiences of our customers show that still some dogs (less than 10%) do react on Curogan with a discolouration.- A further advantage of Curogan is the fact it is absolutely free of nickel.