JANNIK Herm Sprenger 4.00 mm x 20" X-Large Black Stainless Steel Pinch Training Collar, One Size Herm Sprenger 6427B | Prong Training Collar | Anodized Black Stainless Steel | Ten (10) 4 mm Prong Links. Classic comfort version style with assembly chain for professional dog training. Center plate assembly from which five prong links are linked on both sides of center plate with prong links placed directional toward martingale chain, placing even pressure on the neck sides and not on the trachea. Prong ends are beveled and polished. This model is placed around neck by pinching or disconnecting a prong. Initial purchase size fits neck size up to approximately 16 to 18 inches depending on fur type and fur depth. Collar opens to approximately 20 inches. Prong links can be added and removed to adjust fit. Additional prong links can be purchased separately. Read Product Description for additional instructions for sizing, fit, and care.