Metal Plates Martingale Dog Collar 3mm Link Chrome Made of high quality chrome plated steel for durability and resistance to rust and tarnishing Limited closure ensures dog's safety Metal plates; 3mm link chain. Variations with link connection are 7/8" wide; variations with plate connection are 1" wide Sizes specified in all the way opened and closed positions. Available in 6 sizes For proper size please measure the circumference of dog's neck and make sure it is not less than "closed" measurement. Also make sure you choose a size (open position) that will fit over the dogs head