Standard size: 25" (63 cm) will fit dogs with 23" (58 cm) neck size. For a smaller or larger one remove or add extra links. 1 link adds: 1.6" (4 cm) Prongs diameter: 1/6" (4 mm) suits for dogs up to 155 lbs (70 kg) The Herm Sprenger prong collar with quick release is a training tool to control your dog while daily walks or training sessions. The prongs pinch dog's neck slightly once he pulls on a leash. The Herm Sprenger prong collar is produced of rustproof chrome-plated steel. It's equipped with a quick release snap hook to take on/off the collar with ease. And there is a swivel for leash attachment. Measure your dog carefully behind the dog's ears and under the jaw line. A dog prong collar should be approximately 2 inch larger than a dog's neck.