Chrome Pinch Training Prong Dog Collar 4 Size Sizes specified in all the way opened and closed positions. Available in 4 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 Made of high quality chrome plated steel for durability and resistance to rust and tarnishing Practical and easy to use, provide an effective alternative to choke chains Size 1 - 2.5mm link; Size 2 - 3mm link; Size 3 - 3.3mm link; Size 4 - 3.3mm link;