The Aviator Harness Leash are made from high quality nylon and rubber shock cords that expand as much as 100% depending upon the health and strength of your parrots or birds.for all Medium birds size :*Eclectus, Med.*Macaws (Severe, Red Fronted) Lg.*Amazons (Double Yellow, Yellow Nape),*Umbrella Cockatoo,*Congo Grey,*Solomon Island Eclectus.*Escape-Proof